Polyester resin compositions, polyester film, and magnetic recording medium

ABSTRACT

A polyester composition produced without using an antimony compound as a polycondensation catalyst and including (I) a composition containing, on a weight basis, 30 ppm or less of antimony, 0.5 to 50 ppm of titanium, and 0.1 to 100 ppm of phosphorus, in which the number density of titanium-containing particles, the equivalent circular diameter of which is 1 μm or more, is less than 100/0.02 mg; and (II) a composition containing, on a weight basis, antimony, titanium and phosphorous as defined above, in which organic polymer particles are contained in amount of 0.1 to 5 wt %, the organic polymer particles having an average particle diameter determined by dynamic light scattering of 0.05 to 3 μm and containing 0.01% or less of coarse particles relative to the total number of the particles, the coarse particles having a diameter at least twice the average particle diameter.

This application is a division of application Ser. No. 10/529,847, filedJun. 13, 2005, which is a 371 of international applicationPCT/JP2003/012708, filed Oct. 3, 2003, which claims priority based onJapanese Patent Application Nos. 2002-291092 and 2002-349521, filed Oct.3, 2002, and Dec. 2, 2002, respectively, and which are incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to polyester resin compositions, catalystsfor producing polyesters, polyester films, and magnetic recording media.

BACKGROUND ART

Polyesters, in particular, polyethylene terephthalate, have excellentmechanical properties, such as crystallinity and strength, chemicalresistance, thermal properties, electrical properties, and transparency,and are thus used in various industrial applications, such as films,fibers, bottles, and extrusion-molded products. The demand therefor isgrowing. In particular, polyesters are used in the field of filmapplications, for example, magnetic recording applications, agriculturalapplications, packaging applications, capacitor applications, andconstruction materials applications where there are massive demands, dueto their superior mechanical properties and economic efficiency.

For example, polyethylene terephthalate is produced from ethylene glycoland terephthalic acid or its ester-forming derivative. In general,commercial processes for producing polymers with high molecular weightcommonly use antimony-based compounds as polycondensation catalysts.

However, antimony-based compounds have the following problems.

For example, antimony-based compounds partly evaporate and dissipateduring polymer melting processes and their residues deposit around thedies and induce surface defects in films.

Antimony-based compounds tend to form relatively large particles inpolymers and thus cause an increased filtration pressure at filters,surface defects in films during film-making, and breaking of films undersevere conditions.

Use of antimony-based compounds impairs the stability of particles addedto polymers, thereby causing agglomeration of particles. This results indecreased quality, such as generation of coarse projections in surfaces,and decreased operation efficiency due to increased filtration pressuresat filters, as described above.

Accordingly polyesters containing small amounts of antimony or free ofantimony are desired.

Known examples of compounds other than antimony-based compounds that canfunction as polycondensation catalysts are germanium-based compounds.However, germanium-based compounds are quite expensive and thus notsuitable for common usage.

Other than antimony-based compounds and germanium-based compounds,titanium-based compounds are known.

For example, Japanese Unexamined Patent Application Publication No.2002-187942 discloses a method of processing a titanium compound withwater containing an alkaline compound, an organic solvent, or a mixturethereof before adding the titanium compound to the reaction system inthe polyester polymerization step.

Japanese Unexamined Patent Application Publication No. 2000-119383discloses a polyester polymerization catalyst composed of titaniumdioxide having an average primary particle diameter of 100 nm or less.

Japanese Unexamined Patent Application Publication No. 2000-17065discloses a polyester composition composed of a high-purity dicarboxylicacid component and a titanium compound.

Japanese Unexamined Patent Application Publication No. 10-316749discloses a method for producing a polyester resin in which a productprepared by heating a mixture of an organotitanium compound and anorganotin compound is used as a catalyst.

Japanese Unexamined Patent Application Publication No. 63-278927discloses a method for producing polyester using a particular amount ofa manganese compound, and an alkali metal compound, a phosphoruscompound, or an organotitanium compound.

Japanese Unexamined Patent Application Publication No. 54-43294discloses a method for producing a polyester from a zinc compound, acobalt compound, an aromatic multivalent carboxylic acid, and tetraalkyltitanate.

Japanese Unexamined Patent Application Publication No. 54-37196discloses a method for producing polyester, including performingtransesterification between a particular amount of a manganese compoundand a cobalt compound and then performing polymerization in the presenceof a catalyst, which is a reaction product between an aromaticmultivalent carboxylic acid and tetraalkyl titanate.

Japanese Unexamined Patent Application Publication No. 51-81896discloses a method of combining a tellurium compound, a cobalt compound,and a cobalt salt of a phosphorus compound in the presence of a titaniumoxide acting as a catalyst.

Japanese Unexamined Patent Application Publication No. 51-81895discloses a method of combining a bismuth compound, a cobalt compound,and a cobalt salt of a phosphorus compound in the presence of a titaniumoxide acting as a catalyst.

Japanese Unexamined Patent Application Publication No. 51-66395discloses a method of adding a nickel compound in the presence of atitanium oxide acting as a catalyst.

Japanese Unexamined Patent Application Publication No. 7-292087discloses a polyester in which the content of the metal precipitatedparticles derived from a titanium catalyst is controlled to a particularvalue or lower.

However, these techniques cannot prevent titanium compounds (polyesterpolymerization catalyst) from forming debris by deterioration oragglomeration during polyester polymerization reaction. Although it ispossible to reduce debris, these techniques cannot prevent formation ofcoarse particles. For example, these techniques do not achievesufficient effects as films for magnetic recording media applicationsthat require particularly smooth and flat surfaces.

Films for magnetic recording media or the like commonly containparticles for enhancing the film slidability and film surfaceproperties. For example, Japanese Unexamined Patent ApplicationPublication No. 59-217755 discloses that the use of organic polymerparticles highly compatible with polyesters is preferable. However, thistechnique is not sufficient for reducing coarse projections in filmsurfaces.

When titanium-based compounds are used as polycondensation catalysts,yellow polyesters are obtained as a result. Moreover, thermal stabilityof the polymer melted by heating is decreased, and film ruptures and thelike occur, thereby decreasing productivity.

In order to overcome the problem of yellow coloration, cobalt compoundsare commonly added to polyesters to reduce yellowness; however, cobaltcompounds decrease thermal stability of the polyesters. Accordingly, thethermal stability of the melted polymer is further decreased, and theproductivity is also decreased.

In order to overcome the problem of heat resistance and color toneassociated with titanium-based catalysts, International Publication No.95/18839 pamphlet discloses a method that uses a complex oxide oftitanium and silicon as a catalyst.

Japanese Unexamined Patent Application Publication No. 2001-89557discloses a titanium-compound catalyst synthesized by hydrolyzing atitanium halide.

However, these techniques do not improve hue as much as to be sufficientfor films for optical applications, for example, where even minutedifferences in hue should be avoided. Moreover, the dispersibility ofthe hue-adjusting agent is low, thereby leading to problems such asscattering and generation of debris.

The present invention aims to provide a practical polyester that can beprepared substantially without using an antimony-based compound as apolycondensation catalyst.

DISCLOSURE OF INVENTION

The features of the present invention are as follows:

[1] A polyester resin composition comprising, on a weight basis, 30 ppmor less of antimony, 0.5 to 50 ppm of titanium, and 0.1 to 100 ppm ofphosphorus, wherein the number density of titanium-containing particles,the equivalent circular diameter of which is 1 μm or more, is less than100/0.02 mg.[2] The polyester resin composition according to [1] above, wherein atitanium compound is used as a polymerization catalyst.[3] The polyester resin composition according to [1] or [2] above,comprising a titanium oxide.[4] The polyester resin composition according to [3] above, comprising acomplex oxide of titanium and silicon.[5] The polyester resin composition according to one of [1] to [4]above, comprising a titanium compound having at least one substituentselected from the group consisting of an alkoxy group, a phenoxy group,an acylate group, an amino group, and a hydroxyl group.[6] The polyester resin composition according to [5] above, wherein thealkoxy group in the titanium compound is at least one functional groupselected from the group consisting of a β-diketone-system functionalgroup, a hydroxycarboxylic acid-system functional group, and aketoester-system functional group.[7] The polyester resin composition according to [5] above, wherein theacylate group in the titanium compound is either a multivalentcarboxylic acid-system functional group or a nitrogen-containingmultivalent carboxylic acid-system functional group.[8] The polyether resin composition according to [5] above, wherein thetitanium compound has an aliphatic alkoxy group or an aliphatic acylategroup.[9] The polyether resin composition according to one of [1] to [8]above, comprising at least one phosphorus-based compound selected fromthe group consisting of a phosphoric acid-based compound, a phosphorousacid-based compound, a phosphonic acid-based compound, a phosphinicacid-based compound, a phosphine oxide-based compound, a phosphonousacid-based compound, a phosphinous acid-based compound, and aphosphine-based compound.[10] The polyester resin composition according to [9] above, comprisingphosphoric acid and/or a phosphate compound.[11] The polyester resin composition according to [9] above, comprisinga phosphonic acid compound and/or a phosphonate compound.[12] The polyester resin composition according to [11] above, whereinthe phosphorus-based compound is ethyl diethylphosphonoacetate.[13] The polyester resin composition according to one of [1] to [12]above, wherein the molar ratio of titanium to phosphorus (Ti/P) is inthe range of 0.1 to 20.[14] The polyester resin composition according to [1] to [13] above,further comprising 5 to 100 ppm of an alkaline earth metal element on aweight basis.[15] The polyester resin composition according to [14], comprising 15 to60 ppm of magnesium on a weight basis.[16] The polyester resin composition according to one of [1] to [15]above, wherein the specific volume resistivity is in the range of 1×10⁶to 1×10⁹ Ω·cm when melted.[17] A polyester film comprising the polyester resin compositionaccording to one of [1] to [16] above.[18] A laminated polyester film comprising a plurality of layers atleast one of which comprises the polyester resin composition accordingto one of [1] to [16] above.[19] A magnetic recording medium, comprising the laminated polyesterfilm according to [18].([1] to [19] are referred to as Invention Group I)[20] A polyester resin composition comprising, on a weight basis, 30 ppmor less of antimony, 0.5 to 50 ppm of titanium, and 0.1 to 100 ppm ofphosphorus, wherein organic polymer particles are contained in amount of0.1 to 5 wt %, the organic polymer particles having an average particlediameter determined by dynamic light scattering of 0.05 to 3 μm andcontaining 0.01% or less of coarse particles relative to the totalnumber of the particles, the coarse particles having a diameter at leasttwice the average particle diameter.[21] The polyester resin composition according to [20] above, wherein atitanium compound is used as a polymerization catalyst.[22] The polyester resin composition according to [20] or[21] above, comprising a titanium oxide.[23] The polyester resin composition according to [22] above, comprisinga complex oxide of titanium and silicon.[24] The polyester resin composition according to one of [20] to [23]above, comprising a titanium compound having at least one substituentselected from the group consisting of functional groups represented byformulae 1 to 6 below:

(wherein R₁ to R₉ each represent hydrogen or a C₁-C₃₀ hydrocarbongroup).[25] The polyester resin composition according to [24] above, wherein atleast one of R₁ to R₉ in formulae 1 to 6 is a C₁-C₃₀ hydrocarbon grouphaving an alkoxy group, a hydroxyl group, a carbonyl group, an acetylgroup, a carboxyl group, an ester group, or an amino group.[26] The polyester resin composition according to [25] above, wherein atleast one of R₁ to R₆ in formulae 1 to 3 is a C₁-C₃₀ hydrocarbon grouphaving a hydroxyl group, a carbonyl group, an acetyl group, a carboxylgroup, or an ester group.[27] The polyester resin composition according to [25] above, wherein atleast one of R₁ to R₃ in formula 1 is a C₁-C₃₀ hydrocarbon group hayinga carboxyl group or an ester group.[28] The polyester resin composition according to [25], wherein R₇ informula 4 is a C₁-C₃₀ hydrocarbon group.[29] The polyester resin composition according to [28], wherein R₇ informula 4 represents a C₁-C₃₀ hydrocarbon group having a hydroxyl group,a carbonyl group, an acetyl group, a carboxyl group, or an ester group.[30] The polyester resin composition according to one of [20] to [29]above, comprising at least one phosphorus-based compound selected fromthe group consisting of a phosphoric acid-based compound, a phosphorousacid-based compound, a phosphonic acid-based compound, a phosphinicacid-based compound, a phosphine oxide-based compound, a phosphonousacid-based compound, a phosphinous acid-based compound, and aphosphine-based compound.[31] The polyester resin composition according to [30] above, comprisingphosphoric acid and/or a phosphate compound.[32] The polyester resin composition according to [30] above, comprisinga phosphonic acid compound and/or a phosphonate compound.[33] The polyester resin composition according to [32] above, whereinthe phosphorus-based compound is ethyl diethylphosphonoacetate.[34] The polyester resin composition according to one of [20] to [33]above, wherein the molar ratio of titanium to phosphorus (Ti/P) is inthe range of 0.1 to 20.[35] The polyester resin composition according to one of [20] to [34]above, further comprising 5 to 100 ppm of an alkaline earth metalelement on a weight basis.[36] The polyester resin composition according to [35] above, comprising15 to 60 ppm of magnesium on a weight basis.[37] The polyester resin composition according to one of [20] to [36]above, wherein the organic polymer particles have a degree ofcross-linking of at least 50%.[38] The polyester resin composition according to one of [20] to [37]above, wherein the organic polymer particles are avinylbenzene-divinylbenzene copolymer.[39] The polyester resin composition according to one of [20] to [38]above, wherein 0.1 to 5 wt % of a water-soluble polymer relative to theorganic polymer particles is contained.[40] The polyester resin composition according to [39], wherein thewater-soluble polymer has a pyrrolidone residue.[41] The polyester resin composition according to one of [20] to [40]above, wherein the specific volume resistivity is in the range of 1×10⁶to 1×10⁹ Ω·cm when melted.[42] A polyester film comprising the polyester resin compositionaccording to one of [20] to [41] above.[43] A laminated polyester film comprising a plurality of layers atleast one of which comprises the polyester resin composition accordingto one of [20] to [41].[44] A magnetic recording medium, comprising the laminated polyesterfilm according to [43].([20] to [44] are referred to as Invention Group II)[45] A catalyst for producing polyesters, comprising a reaction productbetween at least one compound selected from the group consisting of thecompounds represented by general formulae 7 and 8 below and a ligandcomprising at least one type of atom selected from the group consistingof a nitrogen atom, a sulfur atom, and an oxygen atom as the donor atom,and being capable of coordinating with two or more sites:

Ti(OR)₄  (Formula 7)

Ti(OH)_(m)(OR)_(4-m)  (Formula 8)

(wherein Rs may be the same or different and each represent C₂-C₁₀organic group, and m represents an integer of 1 to 4).[46] The catalyst for producing polyesters according to [45] above,wherein the organic group R is an alkyl group.[47] The catalyst for producing polyesters according to [45] or [46]above, wherein the compound represented by general formula 7 or 8 is atetraalkoxytitanium compound or a titanium chelate compound.[48] The catalyst for producing polyesters according to one of [45] to[47] above, wherein the ligand is at least one compound selected fromthe group consisting of metal-free phthalocyanine, indanthrone,anthraquinone, and methine.[49] A polyester resin composition produced in the presence of thecatalyst for producing polyesters according to one of [45] to [48]above.[50] A polyester film comprising the polyester resin compositionaccording to [49].[51] A laminated polyester film comprising a plurality of layers, atleast one of which comprises the polyester resin composition accordingto [49] above.[52] A magnetic recording medium, comprising the laminated polyesterfilm according to [51] above.([45] to [52] are referred to as Invention Group III)

Invention Groups I to III can provide a polyester having excellentslidability and thermal stability and suitable for practicalapplications including magnetic recording medium applications by usingsubstantially no antimony-based compound as a polycondensation catalyst.

(Invention Group III)

Invention Group III can provide a polyester that has satisfactory hue.

BEST MODE FOR CARRYING OUT THE INVENTION Invention Groups I to III

Polyesters are polymers synthesized from dicarboxylic acid or itsester-forming derivative and diol or its ester-forming derivative.

Examples of the dicarboxylic acid include aromatic dicarboxylic acidssuch as terephthalic acid, isophthalic acid, phthalic acid,1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid,2,6-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid,4,4′-diphenyletherdicarboxylic acid, 4,4′-diphenylsulfonedicarboxylicacid, and 5-sodium sulfoisophthalic acid; aliphatic dicarboxylic acids,such as dimer acid, adipic acid, and sebacic acid; and alicyclicdicarboxylic acids such as cyclohexanedicarboxylic acid. Theester-forming derivatives thereof may also be used.

Examples of the diol include aliphatic, alicyclic, and aromatic diols,such as ethylene glycol, 1,3-propanediol, 1,2-propanediol, neopentylglycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol,1,4-cyclohexanedimethanol, diethylene glycol, triethylene glycol,polyalkylene glycol, 2,2-bis(4′-β-hydroxyethoxyphenyl)propane, andethylene oxide adducts of bisphenol A.

These components may be used alone or in combination.

In addition, hydroxycarboxylic acid, such as parahydroxybenzoic acid,and its ester-forming derivative may be used.

Examples of polyesters include, polyethylene terephthalate, polybutyleneterephthalate, polycyclohexanedimethylene terephthalate,polytrimethylene terephthalate (a.k.a., polypropylene terephthalate),polyethylene naphthalate, andpolyethylene-1,2-bis(2-chlorophenoxy)ethane-4,4′-dicarboxylate. Amongthese, polyethylene terephthalate or a polyester copolymer containingethylene terephthalate units as the main units are preferable due totheir versatility. The comonomers for the copolymer may be adequatelyselected from the dicarboxylic acids and diols mentioned above.

In the present invention, a “catalyst” refers to a substance thatsubstantially contributes to promoting all of the reactions (1) to (3)below or some of their elementary reactions:

(1) esterification reaction between a dicarboxylic acid component and adiol component;(2) transesterification reaction between an ester-forming derivative ofa dicarboxylic acid and a diol component; and(3) polycondensation reaction for increasing the degree ofpolymerization of low-grade polyethylene terephthalate produced by theesterification reaction or the transesterification reaction after thereaction is substantially terminated.

It should be noted here that titanium oxide particles commonly used asinorganic particles for in fiber delustering agents and the like havesubstantially no catalytic effect to the reactions mentioned above.Thus, they are different from the titanium compound described below,which functions as a catalyst in the present invention.

(Invention Groups I and II)

It is important that the polyester resin compositions of the InventionGroups I and II contain 30 ppm or less of antimony on a weight basis. Inthis manner, contamination of dies during molding, filter clogging, andgeneration of debris can be reduced, and polymers can be produced at lowcosts. The antimony content is more preferably 10 ppm or less and mostpreferably substantially zero.

It is important that the polyester resin compositions of the InventionGroups I and II contain titanium. Titanium is derived from a titaniumcompound used as a polymerization catalyst. In other words, thepolyester resin composition of the Invention Groups I and II arepreferably prepared in the presence of a titanium compound acting as apolymerization catalyst.

It is important that the titanium content in the resin composition,i.e., the amount of the titanium compound used as the polymerizationcatalyst in terms of titanium, be in the range of 0.5 to 50 ppm,preferably 1 to 30 ppm, and most preferably 3 to 20 ppm, on a weightbasis. Within these ranges, polymerization activity is high, and thermalstability and hue of the resulting polymer are satisfactory. At atitanium content of less than 0.5 ppm, the polymerization activity isnot sufficient. At a titanium content exceeding 50 ppm, debris derivedfrom the titanium catalyst is easily produced, and the resultingpolyester exhibits low heat resistance.

A preferred example of the titanium compound is a titanium oxide. Inparticular, a complex oxide of titanium and silicon and ultra fineparticles of titanium oxide are preferable from the standpoints ofpolymerization activity and reduced formation of debris. The complexoxide of titanium and silicon may contain other metal elements.

The titanium oxide may be obtained by, for example, hydrolyzing analkoxide compound of titanium.

The complex oxide may be synthesized by, for example, a coprecipitationmethod, a partial hydrolysis method, or a coordination chemistry sol-gelmethod from a main starting material, i.e., a titanium alkoxidecompound, in the presence of small amounts of alkoxide compounds ofother metals, such as silicon and zirconium, or a polyhydric alcoholcompound. Here, the coprecipitation method refers to a method in which asolution containing two or more components and having a predeterminedcomposition is prepared, and this solution is hydrolyzed whilemaintaining this composition. The partial hydrolysis method refers to amethod in which one component is hydrolyzed in advance, and to thiscomponent, the other component is added to further conduct hydrolysis.The coordination chemistry sol-gel method refers to a method in which atitanium alkoxide row material is preliminarily reacted with apolyhydric alcohol compound or the like having a plurality of functionalgroups in a molecule to control the speed of the subsequent hydrolysisreaction by the reaction product. These methods for synthesizingcompounds are disclosed in, for example, Ueno et al., “Kinzokuarukokishido wo mochiiru shokubai chousei (Catalyst Preparation withMetal Alkoxide)”, p. 321, line 1 to p. 353, line 16, IPC, Aug. 10, 1993.

The molecular weight of the titanium oxide super fine particles usableas a polymerization catalyst is preferably lower than 100,000 g/mol fromthe standpoint of catalytic activity and prevention of debris. Themolecular weight of the titanium oxide super fine particles is morepreferably 500 to 100,000 g/mol, yet more preferably 1,000 to 50,000g/mol, and most preferably 1,500 to 20,000 g/mol.

Titanium oxides having at least one substituent selected from the groupconsisting of an alkoxy group, a phenoxy group, an acylate group, anamino group, and a hydroxyl group are also preferable as thepolymerization catalyst.

Examples of the alkoxy group include tetraalkoxy groups such astetraethoxide, tetrapropoxide, tetraisopropoxide, tetrabutoxide, andtetra-2-ethylhexoxide. Examples of alkoxy groups in a broader sense,i.e., alkoxy groups having the organic group bonded to a titanium atomvia an oxygen atom, include β-diketone-system functional groups such asacetylacetone; multivalent hydroxycarboxylic acid-system groups such aslactic acid, malic acid, tartaric acid, salicylic acid, and citric acid;and ketoester-system functional groups such as methyl acetoacetate andethyl acetoacetate. Aliphatic alkoxy groups are particularly preferablefrom the standpoint of suppressing the formation of debris.

Examples of the phenoxy groups include phenoxy and cresylate.

Examples of the acylate groups include tetraacylates such as lactate andstearate; multivalent carboxylic acid-system groups such as phthalicacid, trimellitic acid, trimesic acid, hemimellitic acid, pyromelliticacid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipicacid, sebacic acid, maleic acid, fumaric acid, cyclohexanedicarboxylicacid, and anhydrides thereof; nitrogen-containing multivalent carboxylicacid-system functional groups such as ethylenediaminetetraacetic acid,nitrilotripropionic acid, carboxyiminodiacetic acid,carboxymethyliminodipropionic acid, diethylenetriaminopentaacetic acid,triethylenetetraamine hexaacetic acid, iminodiacetic acid,iminodipropionic acid, hydroxyethyliminodiacetic acid,hydroxyethyliminodipropionic acid, and methoxyethyliminodiacetic acid.Aliphatic acylate groups are particularly preferred from the standpointof preventing formation of debris.

Examples of the amino groups include aniline, phenylamine, anddiphenylamine.

Di-isopropoxy bis-acetylacetone, triethanolaminate isopropoxide, or thelike containing two of these functional groups may be used.

Among these titanium compounds, tetraalkoxytitanium compounds andtitanium acylate compounds are preferable from the standpoint ofpreventing formation of debris.

Titanium compounds having at least one substituent selected from thefunctional groups represented by formulae 1 to 6 below are preferablefrom the standpoint of preventing formation of debris:

wherein R₁ to R₉ in formulae 1 to 6 each represent a hydrogen or aC₁-C₃₀ hydrocarbon group.

Preferably, at least one of R₁ to R₉ in formulae 1 to 6 is a C₁-C₃₀hydrocarbon group having an alkoxy group, a hydroxyl group, a carbonylgroup, an acetyl group, a carboxyl group, an ester group, or an aminogroup.

Preferably, at least one of R₁ to R₆ in formulae 1 to 3 is a C₁-C₃₀hydrocarbon group having a hydroxyl group, a carbonyl group, an acetylgroup, a carboxyl group, or an ester group.

Preferably, at least one of R₁ to R₃ in formula 1 is a C₁-C₃₀hydrocarbon group having a carboxyl group or an ester group.

Preferably, R₇ in formula 4 is a C₁-C₃₀ hydrocarbon group.

Preferably, R₇ in formula 4 represents a C₁-C₃₀ hydrocarbon group havinga hydroxyl group, a carbonyl group, an acetyl group, a carboxyl group,or an ester group.

Examples of the functional group represented by formula 1 include alkoxygroups such as ethoxide, propoxide, isopropoxide, butoxide, and2-ethylhexoxide, and multivalent hydroxycarboxylic acid-system compoundssuch as lactic acid, malic acid, tartaric acid, and citric acid.

Examples of the functional group represented by formula 2 includeβ-diketone-system compounds such as acetylacetone and ketoester-systemcompounds such as methyl acetoacetate and ethyl acetoacetate.

Examples of the functional group represented by formula 3 includephenoxy, cresylate, and salicylic acid.

Examples of the functional group represented by formula 4 includeacylate groups such as lactate and stearate; multivalent carboxylicacids such as phthalic acid, trimellitic acid, trimesic acid,hemimellitic acid, pyromellitic acid, oxalic acid, malonic acid,succinic acid, glutaric acid, adipic acid, sebacic acid, maleic acid,fumaric acid, cyclohexanedicarboxylic acid, and anhydrides thereof; andnitrogen-containing multivalent carboxylic acids such asethylenediaminetetraacetic acid, nitrilotripropionic acid,carboxylminodiacetic acid, carboxymethyliminodipropionic acid,diethylenetriaminopentaacetic acid, triethylenetetraamine hexaaceticacid, iminodiacetic acid, iminodipropionic acid,hydroxyethyliminodiacetic acid, hydroxyethyliminodipropionic acid, andmethoxyethyliminodiacetic acid.

Examples of the functional group represented by formula 5 includeaniline, phenylamine, and diphenylamine.

Preferably, the substituent represented by formula 1 and/or formula 4 iscontained from the standpoint of thermal stability and hue of theresulting polymer.

Examples of the titanium compound containing two or more or thesubstituents represented by formulae 1 to 6 include titaniumdi-isopropoxy bis-acetylacetonate and titanium triethanolaminateisopropoxide.

It is important that the polyester resin compositions of the InventionGroups I and II contain phosphorus. Production of polyesters usesphosphorus-based compounds as aids for controlling the catalyticactivity and increasing the heat resistance of the resulting polymer.Phosphorus in the polyester resin compositions is derived from thephosphorus-based compounds used.

It is important that the phosphorus content in the resin composition,i.e., the amount of the phosphorus-based compound used in terms ofphosphorus, be in the range of 0.1 to 100 ppm on a weight basis. At acontent less than 0.1 ppm, formation of debris easily occurs due to thecatalyst, and the hue and heat resistance of the resulting polyester aredegraded. In contrast, at a content exceeding 100 ppm, formation ofdebris easily occurs due to the catalyst, and the polymerizationreaction requires a longer time, thereby decreasing the productivity.The phosphorus content is preferably 1 to 80 ppm, more preferably 3 to50 ppm, yet more preferably 3 to 35 ppm, and most preferably 3 to 20 ppmfrom the standpoint of thermal stability during yarn-making orfilm-making and hue of the polyester.

The phosphorus-based compound is preferably at least one selected fromthe group consisting of a phosphoric acid-based compound, a phosphorousacid-based compound, a phosphonic acid-based compound, a phosphinicacid-based compound, a phosphine oxide-based compound, a phosphonousacid-based compound, a phosphinous acid-based compound, and aphosphine-based compound from the standpoint of thermal stability,suppression of debris, and improving hue. Phosphoric acid-based andphosphonic acid-based compounds are particularly preferable from thesame standpoint.

Examples of phosphoric acid-based compound include phosphoric acid andphosphate compounds such as trimethyl phosphate, triethyl phosphate, andtriphenyl phosphate. Among the phosphoric acid-based compounds,phosphoric acid and phosphate compounds are preferable from thestandpoint of thermal stability, suppression of debris, and improvementof hue. In other words, the polyester resin compositions of theInvention Groups I and II preferably contain phosphoric acid and/or aphosphate. In the present invention, the phrase “and/or” means eitherone of the two can be used alone or both may be used in combination.

Examples of the phosphorous acid-based compounds include phosphorousacid, trimethyl phosphite; triethyl phosphite, and triphenyl phosphite.

Among the phosphonic acid-based compounds, phosphonic acid compounds andphosphonate compounds are preferable from the standpoints of thermalstability, suppression of debris, and improvement of hue. In otherwords, the polyester resin compositions of the Invention Groups I and IIpreferably contain phosphonic acid compounds and/or phosphonatecompounds.

Examples of the phosphonic acid compound include, methylphosphonic acid,ethylphosphonic acid, propylphosphonic acid, isopropylphosphonic acid,butylphosphonic acid, phenylphosphonic acid, benzylphosphonic acid,tolylphosphonic acid, xylylphosphonic acid, biphenylphosphonic acid,naphthylphosphonic acid, anthrylphosphonic acid,2-carboxyphenylphosphonic acid, 3-carboxyphenylphosphonic acid,4-carboxyphenylphosphonic acid, 2,3-dicarboxyphenylphosphonic acid,2,4-dicarboxyphenylphosphonic acid, 2,5-dicarboxyphenylphosphonic acid,2,6-dicarboxyphenylphosphonic acid, 3,4-dicarboxyphenylphosphonic acid,3,5-dicarboxyphenylphosphonic acid, 2,3,4-tricarboxyphenylphosphonicacid, 2,3,5-tricarboxyphenylphosphonic acid,2,3,6-tricarboxyphenylphosphonic acid, 2,4,5-tricarboxyphenylphosphonicacid, and 2,4,6-tricarboxyphenylphosphonic acid.

Examples of the phosphonate include dimethyl methylphosphonate, diethylmethylphosphonate, dimethyl ethylphosphonate, diethyl ethylphosphonate,dimethyl phenylphosphonate, diethyl phenylphosphonate, diphenylphenylphosphonate, dimethyl benzylphosphonate, diethylbenzylphosphonate, diphenyl benzylphosphonate, lithium(ethyl3,5-di-tert-butyl-4-hydroxybenzylphosphonate), sodium(ethyl3,5-di-tert-butyl-4-hydroxybenzylphosphonate), magnesium bis(ethyl3,5-di-tert-butyl-4-hydroxybenzylphosphonate), calcium bis(ethyl3,5-di-tert-butyl-4-hydroxybenzylphosphonate), diethylphosphonoaceticacid, methyl diethylphosphonoacetate, and ethyl diethylphosphonoacetate.In particular, ethyl diethylphosphonoacetate is preferable from thestandpoints of thermal stability, suppression of debris, and improvementof hue.

Examples of the phosphinic acid-based include hypophosphorous acid,sodium hypophosphite, methylphosphinic acid, ethylphosphinic acid,propylphosphinic acid, isopropylphosphinic acid, butylphosphinic acid,phenylphosphinic acid, tolylphosphinic acid, xylylphosphinic acid,biphenylphosphinic acid, diphenylphosphinic acid, dimethylphosphinicacid, diethylphosphinic acid, dipropylphosphinic acid,diisopropylphosphinic acid, dibutylphosphinic acid, ditolylphosphinicacid, dixylylphosphinic acid, dibiphenylphosphinic acid,naphthylphosphinic acid, anthrylphosphinic acid,2-carboxyphenylphosphinic acid, 3-carboxyphenylphosphinic acid,4-carboxyphenylphosphinic acid, 2,3-dicarboxyphenylphosphinic acid,2,4-dicarboxyphenylphosphinic acid, 2,5-dicarboxyphenylphosphinic acid,2,6-dicarboxyphenylphosphinic acid, 3,4-dicarboxyphenylphosphinic acid,3,5-dicarboxyphenylphosphinic acid, 2,3,4-tricarboxyphenylphosphinicacid, 2,3,5-tricarboxyphenylphosphinic acid,2,3,6-tricarboxyphenylphosphinic acid, 2,4,5-tricarboxyphenylphosphinicacid, 2,4,6-tricarboxyphenylphosphinic acid,bis(2-carboxyphenyl)phosphinic acid, bis(3-carboxyphenyl)phosphinicacid, bis(4-carboxyphenyl)phosphinic acid,bis(2,3-dicarboxyphenyl)phosphinic acid,bis(2,4-dicarboxyphenyl)phosphinic acid,bis(2,5-dicarboxyphenyl)phosphinic acid,bis(2,6-dicarboxyphenyl)phosphinic acid,bis(3,4-dicarboxyphenyl)phosphinic acid,bis(3,5-dicarboxyphenyl)phosphinic acid,bis(2,3,4-tricarboxyphenyl)phosphinic acid,bis(2,3,5-tricarboxyphenyl)phosphinic acid,bis(2,3,6-tricarboxyphenyl)phosphinic acid,bis(2,4,5-tricarboxyphenyl)phosphinic acid,bis(2,4,6-tricarboxyphenyl)phosphinic acid, methyl methylphosphinate,methyl dimethylphosphinate, ethyl methylphosphinate, ethyldimethylphosphinate, methyl ethylphosphinate, methyl diethylphosphinate,ethyl ethylphosphinate, ethyl diethylphosphinate, methylphenylphosphinate, ethyl phenylphosphinate, phenyl phenylphosphinate,methyl diphenylphosphinate, ethyl diphenylphosphinate, phenyldiphenylphosphinate, methyl benzylphosphinate, ethyl benzylphosphinate,phenyl benzylphosphinate, methyl bisbenzylphosphinate, ethylbisbenzylphosphinate, and phenyl bisbenzylphosphinate.

Examples of the phosphine oxide system include trimethylphosphine oxide,triethylphosphine oxide, tripropylphosphine oxide, triisopropylphosphineoxide, tributylphosphine oxide, and triphenylphosphine oxide.

Examples of the phosphonous acid-based include methylphosphonous acid,ethylphosphonous acid, propyl phosphonous acid, isopropylphosphonousacid, butylphosphonous acid, and phenylphosphonous acid.

Examples of the phosphinous acid-based include methylphosphinous acid,ethylphosphinous acid, propylphosphinous acid, isopropylphosphinousacid, butylphosphinous acid, phenylphosphinous acid, dimethylphosphinousacid, diethylphosphinous acid, dipropylphosphinous acid,diisopropylphosphinous acid, dibutylphosphinous acid, anddiphenylphosphinous acid.

Examples of the phosphine system include methylphosphine,dimethylphosphine, trimethylphosphine, ethylphosphine, diethylphosphine,triethylphosphine, phenylphosphine, diphenylphosphine, andtriphenylphosphine.

These phosphorus-based compounds may be used alone or in combination.

When the molar ratio of titanium to phosphorus, Ti/P, is in the range of0.1 to 20, the polyester exhibits satisfactory thermal stability andhue. More preferably, Ti/P is in the range of 0.2 to 10, and mostpreferably in the range of 0.3 to 5.

During the polymerization, an alkaline earth metal element is preferablyincorporated from the standpoints of suppression of debris,polymerization activity, and specific volume resistivity of the meltedpolyester resins. The content of the alkaline earth metal element ispreferably in the range of 5 to 100 ppm, more preferably in the range of10 to 80 ppm, and most preferably in the range of 15 to 60 ppm on aweight basis. At a content of 100 ppm or less, formation of debriscontaining titanium can be suppressed.

Among alkaline earth metal elements, calcium and magnesium arepreferable. In particular, magnesium is preferable from the standpointsof suppression of debris and specific volume resistivity of the meltedpolyester resin. Its chlorides and carboxylates are preferable as theadditive compounds. In particular, magnesium acetate is preferable fromthe same standpoints.

The polyester resin compositions of the Invention Groups I and IIpreferably contain manganese. Manganese is derived from a manganesecompound added to the polyester resin composition at a predeterminedstage before the termination of the preparation of the polyester bypolymerization.

The manganese content in the polyester resin composition, i.e., theamount of the manganese compound in terms of manganese, is preferably inthe range of 1 to 400 ppm on a weight basis. The molar ratio ofmanganese to phosphorus, i.e., Mn/P, is preferably in the range of 0.1to 200. In this range, a decrease in polymerization activity can besuppressed, and the hue of the resulting polymer improves. Examples ofthe manganese compound include manganese chloride, manganese bromide,manganese nitrate, manganese carbonate, manganese acetylacetonate,manganese acetate tetrahydrate, and manganese acetate dihydrate.

Moreover, it is preferable to add a cobalt compound at a desired pointduring the process of preparing the polyester resin compositions ofInvention Groups I and II, i.e., to prepare polyester resin compositionscontaining cobalt compounds. In this manner, the hue of the resultingpolymer is improved. Examples of the cobalt compounds include cobaltchloride, cobalt nitrate, cobalt carbonate, cobalt acetylacetonate,cobalt naphthenate, and cobalt acetate tetrahydrate.

The polyester may incorporate an alkali metal compound, an aluminumcompound, a zinc compound, a tin compound, or the like. In this manner,the hue and thermal resistance of the polyester can be improved.

(Invention Group I)

It is important that the number of titanium-containing particles, theequivalent circular diameter of which is 1 μm or more, of each polyesterresin composition of Invention Group I is less than 100 for 0.02 mg ofthe composition. Here, “equivalent circular diameter” refers to adiameter of a circle having the same area as the projected image of aparticle.

These titanium-containing particles are one form of debris mentionedabove. When the number density of such particles is 100 or more, thesurface roughness of the resulting film may increase, and thetransparency of the film may be degraded. The number density of theparticles is preferably 80/0.02 mg or less, and more preferably 50/0.02mg or less. In order to suppress formation of titanium-containingparticles, i.e., formation of debris, it is preferable to suppresshydrolysis of the titanium compound, i.e., the polymerization catalyst,during the polymerization reaction.

(Invention Group II)

It is important that the polyester resin composition of Invention GroupII contain organic polymer particles. Compared to other particles thatcan impart satisfactory winding property and slidability to polyesterfilms, organic polymer particles have higher compatibility to polyestersand relatively uniform particle shape.

The organic polymer particles preferably have an average particlediameter determined by dynamic light scattering of 0.05 to 3 μm, morepreferably 0.1 to 2 μm, and most preferably 0.3 to 1 μm. At an averageparticle diameter exceeding 3 μm, filter clogging easily occurs duringfiltration. At a diameter less than 0.05 μm, satisfactory windingproperty cannot be imparted to the polyester formed into films.

The ratio of the number of coarse particles relative to the total numberof the particles, the coarse particles having a diameter at least twicethe average particle diameter, must be 0.01% or lower, preferably 0.005%or lower, and most preferably 0.001% or loser. When the ratio of thecoarse particles exceeds 0.01%, the number of coarse projections foundin the surface increases, and missing record or the like may occur whenthe film is processed into magnetic recording media.

The content of the organic polymer particles must be 0.1 to 5 wt % ofthe polyester resin composition. The content is more preferably 0.5 to 3wt %, and most preferably 1 to 2 wt %. At a particle content of lessthan 0.1 wt %, the slidability of the resulting film will beinsufficient. At a particle content exceeding 5 wt %, the roughness ofthe film surface becomes excessively high, thereby decreasing flatness.

Examples of the raw materials for the organic polymer particles includecrosslinked polystyrene, silicone, a melamine-formaldehyde copolymer,benzoguanamine, thermosetting epoxy, and crosslinked polyesters. Amongthese, crosslinked polystyrene is preferable. In particular, avinylbenzene-divinylbenzene copolymer is preferable from the standpointsof heat resistance and the polyester compatibility of the particles.

The degree of cross-linking of the organic polymer particles ispreferably at least 50%, preferably at least 65%, and most preferably atleast 80% from the standpoints of heat resistance. Here, the “degree ofcross-linking” of the organic particles refers to a ratio of the weightof the crosslinkable monomer fed to the total weight of the monomers.The crosslinkable monomer is preferably a compound having at least two,and more preferably, exactly two copolymerizable double bonds. Examplesthereof include nonconjugated divinyl compounds such as divinylbenzeneor multivalent acrylate compounds such as trimethylolpropanetrimethacrylate and trimethylolpropane triacrylate.

The organic polymer particles are preferably globular and in particular,spherical in shape since such particles effectively impart slidabilityto the film. The particles may be composite particles (core/shell type),hollow particles, or the like. The particles may be surface-treated bysilane coupling, titanate coupling, or the like.

The polyester resin composition of the Invention Group II preferablycontains a water-soluble polymer to increase the dispersibility fororganic polymer particles.

The content of the water-soluble polymer is preferably in the range of0.1 to 5 wt % relative to the organic polymer particles. The content ismore preferably 0.4 to 3 wt %, and most preferably 0.8 to 2 wt %. At acontent 0.1 wt % or more, the dispersibility for the organic polymerparticles can be improved, and at a content of 5 wt % or less, thepolymer is prevented from producing coarse projections in the filmsurface.

Examples of the water-soluble polymer include polyvinylpyrrolidone,polyvinyl alcohol, and carboxylmethylcellulose. In particular, acompound having a pyrrolidone residue, such as polyvinylpyrrolidone, ispreferable from the standpoint of increasing the dispersibility for theorganic polymer particles.

The water-soluble polymer is preferably combined with an organic polymerparticle slurry and subjected to surface treatment in advance, and thenmelt-mixed with the polyester to yield satisfactory dispersibility.

(Invention Group III)

The catalyst for producing polyesters according to Invention Group IIIcontains a reaction product between at least one compound (hereinafteralso referred to as “compound α) selected from the group consisting ofthe compounds represented by general formulae 7 and 8 below and a ligandcompound containing at least one type of atom selected from the groupconsisting of a nitrogen atom, a sulfur atom, and an oxygen atom as thedonor atom and being capable of coordinating with two or more sites andis hereinafter also referred to as “compound β”:

Ti(OR)₄  (Formula 7)

Ti(OH)_(m)(OR)_(4-m)  (Formula 8)

wherein Rs may be the same or different and each represent C₂-C₁₀organic group, m represents an integer of 1 to 4. R is preferably analkyl group.

For the catalyst for producing polyesters according to Invention GroupIII, it is important that the compound α and the compound β form areaction product in which the compound β is a ligand.

The compound α has activity for polycondensation reaction and functionsas a polymerization catalyst. The compound β improves the hue of theresulting polyester. By using the reaction product between the compoundsα and β as a catalyst, a polyester having excellent hue and heatresistance can be efficiently produced. Here, the ligand compound β iscoordinated with the compound α to form a reaction product. This isclearly distinct from directly adding the ligand compound β to thepolyester to improve the hue. By using the reaction product, problemsthat associated with direct addition of the ligand compound β to thepolyester, i.e., poor dispersibility and scattering to outside thesystem, can be overcome, and the productivity can be increased.

The compound α is preferably a tetraalkoxytitanium compound or atitanium chelate compound.

Examples of the tetraalkoxytitanium compound include tetraisopropyltitanate, tetrabutyl titanate, and tetra(2-ethylhexyl)titanate, andtetramethyl titanate. Among these, tetrabutyl titanate is particularlypreferable.

Examples of the titanium chelate compound include titaniumacetylacetonate, titanium tetraacetylacetonate, titaniumoctyleneglycolate, titanium lactate, titanium ethylacetoacetate,titanium citrate, and titanium ammonium titaniumperoxocitrate. Amongthese, titanium acetylacetonate, titanium citrate, and titanium ammoniumtitaniumperoxocitrate having good reactivity to the ligand compound βare preferable.

The ligand compound β is preferably at least one compound selected fromthe group consisting of indanthrone, anthraquinone, methine, andmetal-free phthalocyanine. An example of indanthrone is one having thestructure represented by A; examples of anthraquinone include thosehaving structures represented by B, C, D, E, and F; an example ofmethine is one having the structure represented by G; and an example ofmetal-free phthalocyanine is one having the structure represented by H:

The molar ratio of the ligand compound β to the compound α in thereaction product preferably satisfies 0.001≦(moles of β/moles of α)≦1.At a ratio of 0.001 or more, the ligand compound β sufficientlyincreases dispersibility and prevents scattering to outside the system.Moreover, the hue can be improved as a result of the coordination. Byadjusting the ratio to 1 or less, polymer is prevented from havingexcessive blue tinge.

The reaction product between the compound α and the ligand compound βcan be prepared by, for example, dissolving the ligand compound β in asolvent, adding the compound α to the resulting solution, and heatingthe reaction system at 0° C. to 200° C. for 10 minutes or more, morepreferably at normal temperature to 150° C., and most preferably at 40°C. to 150° C. for 30 minutes to 2 hours. Alternatively, the mixture ofthe compound α and the compound β may be added to the polyesterpolymerization system without heating.

Examples of the solvent include ethylene glycol, propylene glycol,tetramethylene glycol, and acetic acid. Solvents having highcompatibility to the raw materials for polyesters are preferable.

The reaction product between the compound α and the ligand compound βmay be isolated using an evaporator, a centrifugal separator, a filter,or the like, followed by recrystallization and refining. The refinedproduct may be used as the catalyst.

The polyester resin composition of the Invention Group III is producedin the presence of the catalyst for producing polyesters according tothe Invention Group III.

The amount of the catalyst for producing polyesters relative to thepolyester resin composition according to the Invention Group III ispreferably 1 to 30 ppm in terms of titanium on a weight basis. Byadjusting the amount to 1 ppm or more, sufficient catalytic activity canbe yielded. By adjusting to 30 ppm or less, the polymer can maintainsatisfactory hue and heat resistance; moreover, formation of debris bythe catalyst can be suppressed.

Various catalysts may be used for esterification or transesterificationreaction. For example, acetates such as calcium acetate, magnesiumacetate, and lithium acetate may be used.

It is also preferable to add a phosphorus compound, i.e., a hueadjustor, to the polyester resin composition of the Invention Group III.

Examples of the phosphorus compound include phosphoric acid systems,such as phosphoric acid, monomethylphosphoric acid, monoethylphosphoricacid, and trimethylphosphoric acid; phosphorous acid systems, such asphosphorous acid, dimethyl phosphite, and trimethyl phosphite;phosphonic acid systems, such as phenylphosphonic acid, dimethylphenylphosphonate, dimethylbenzyl phosphonate, dimethylmethyl phosphonate,dipropylmethyl phosphonate, and ethyl diethylphosphonoacetate; andphosphinic acid systems such as diphenylphosphinic acid.

The amount of the phosphorus compound added relative to the polyesterresin composition is preferably 1 to 50 ppm and more preferably 5 to 20ppm in terms of phosphorus on a weight basis. By adjusting the amount to1 ppm or more and preferably 5 ppm or more, change in color due totitanium can be suppressed. By adjusting the amount to 20 ppm or less,the polymerization activity of the catalyst for producing polyesters ofthe Invention Group III can be maintained.

The polyester resin composition of Invention Group III preferablycontains an alkaline earth metal compound. The amount of the alkalineearth metal compound added relative to the polyester resin compositionis preferably 0 to 80 ppm and more preferably 1 to 60 ppm in terms oftotal of the alkaline earth metal elements on a weight basis. Withinthese ranges, the productivity of the polyester resin composition ishigh and heat resistance can be maintained.

(Invention Groups I to III)

The polyester resin compositions of the Invention Groups I to III maycontain, for example, pigments such as titanium oxide, silicon oxide,calcium carbonate, silicon nitride, clay, talc, kaolin, carbon black andthe like; color protection agents; antioxidants, antistatic agents,nucleating agents, inorganic particles, organic particles, viscosityreducers, heat stabilizers, lubricants, infrared absorbers, and UVabsorbers.

The specific volume resistivity of the polyester resin compositions ofInvention Groups I to III when melted is preferably 1×10⁶ to 1×10⁹ Ω·cm,and more preferably 1×10⁷ to 5×10⁸ Ω·cm. In this manner, closely contactbetween the film and the casting drum can be increased byelectro-pinning, thereby preventing air from entering the gaptherebetween. As a result, a film having excellent surface flatness andthickness uniformity can be formed, and film-making rate can beincreased. The specific volume resistivity of the melt can be controlledby adjusting the amount of the alkaline earth metal element andphosphorus relative to the polyester resin. For example, increasing thealkaline earth metal element and decreasing phosphorus tend to decreasethe specific volume resistivity. In contrast, decreasing the alkalineearth metal element and increasing phosphorus tend to increase thespecific volume resistivity.

In general, polyethylene terephthalate, i.e., an example of polyesters,is produced by one of the following processes:

(1) conducting direct esterification using terephthalic acid andethylene glycol as raw materials to obtain a lower polymer and thenconducting polycondensation to obtain a high polymer; and

(2) conducting transesterification using dimethyl terephthalate andethylene glycol as raw materials to obtain a lower polymer and thenconducting polycondensation to obtain a high polymer.

These reactions can be performed by a polymerization method such as abatch process, a semibatch process, or a continuous process.

The esterification in the process (1) above proceeds without anycatalyst; however, the above-described titanium compound may be used asa catalyst. In such a case, the titanium compound may be fed to thereaction system immediately after the raw materials are fed orsimultaneously with the raw materials.

The transesterification of the process (2) above may proceed in thepresence of a catalyst, which may be any of manganese, calcium,magnesium, zinc, and lithium compounds and the titanium compoundsdescribed above.

If a catalyst is used in any of these reactions, a phosphorus compound,which inactivates the reaction catalyst, is added after the reaction issubstantially terminated.

For the Invention Group II, at any desired stage in the process (1) or(2), organic polymer particles or various additives are fed to thesystem, and then a titanium compound, i.e., a polycondensation catalyst,is added to conduct polycondensation to prepare a high molecular-weightpolyethylene terephthalate. Preferably, organic polymer particles andvarious additives are fed to the system after a lower polymer isobtained by esterification in the process (1) or by transesterificationin the process (2).

In the esterification step, it is preferable to add small amounts ofbasic compounds to obtain a polyester resin composition containingsmaller amounts of side reaction products. Examples of the basiccompounds include tertiary amines such as triethylamine, tributylamine,and benzylmethylamine; quaternary amines such as tetraethylammoniumhydroxide, tetrabutylammonium hydroxide, and trimethylbenzylammoniumhydroxide; and potassium hydroxide, sodium hydroxide, potassium acetate,and sodium acetate.

In the polycondensation step, a stabilizer may be added to preventside-reaction such as pyrolysis of polyesters. Examples of thestabilizer includediethyl[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]phosphonate,tetrakis{methylene-3-(dodecylthio)propionate}methane,tetrakis{methylene-(3,5-tert-butyl-4-hydroxyhydrocinnamate)}methane,tridecyl phosphate, tris(2,4-dibutylphenyl)phosphite,tetrakis{methylene-3-(3′,5′-di-tert-butyl-4′-hydroxyphenyl)propionate}methane,and bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol-di-phosphite.These may be used alone or in combination.

The amount of the stabilizer is preferably 0.03 to 2 wt %, and morepreferably 0.05 to 1.9 wt % relative to the resulting polyester resincomposition. At an amount of 0.03 wt % or more, oxidation stability canbe effectively increased. At an amount of 2 wt % or less, obstruction ofpolycondensation can be prevented.

(Invention Group III)

When the stabilizer is preliminary combined with the polyesterpreparation catalyst of the Invention Group III before it is added tothe reaction system, the amount of the stabilizer added is preferably0.003 to 1 wt %. In particular,diethyl[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]phosphonateand bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol-di-phosphiteare suitable for combination with the polyester preparation catalyst ofthe Invention Group III. By adding the stabilizer in an amount in therange of 0.003 to 0.1 wt %, a polyester resin composition havingsatisfactory heat resistance, reduced debris, and desirable hue isobtained.

(Invention Groups I to III)

As is mentioned above, phosphorus compounds inactivate catalysts foresterification and transesterification and are thus supplied to thereaction system after termination of esterification ortransesterification but before polycondensation to control the activityof titanium compounds functioning as catalysts. In such a case, in orderto avoid deactivation of the catalyst resulting from the contact betweenthe titanium compound and the phosphorus compound, a technique ofsupplying the titanium compound and the phosphorus compound to separatereactors, a technique of staggering the timing for supplying thetitanium compound and the phosphorus compound to the same reactor by 1to 15 minutes, or a technique of setting apart the positions at whichthese compounds are fed is preferably employed.

The titanium compound and the phosphorus compound used in the InventionGroups I to III may be directly added to the polyester reaction system.Alternatively, they may be preliminarily combined with a solventcontaining a diol component, such as ethylene glycol or propyleneglycol, of the polyester to prepare solution or slurry and then added tothe reaction system after, if necessary, removal of low boiling pointcomponents, such as alcohol, used during synthesis of the titanium orphosphorus compound. As a result, debris formation in the polymer can besuppressed.

Alternatively, the titanium compound may be reacted with the phosphoruscompound in advance and the product may be used as the catalyst.Examples of such a method include:

(1) A titanium compound is completely or partly dissolved in a solventto prepare a mixture, and a phosphorus compound, is added directly orafter dilution with a solvent to this mixture dropwise; and(2) When a complex in which a ligand is coordinated with a titaniumcompound is to be used, a titanium compound or a ligand compound, suchas a hydroxycarboxylic acid-system compound or a multivalent carboxylicacid-system compound, is completely or partly dissolved in a solvent toprepare a mixture, and a ligand compound or a titanium compound thatforms a complex with the compound is added dropwise to this mixture,either directly or after dilution with a solvent. Subsequently, aphosphorus compound is added dropwise to this mixture either directly orafter dilution with a solvent.

The reaction conditions of the methods (1) and (2) above are preferably0° C. to 200° C. for 1 minute or more and more preferably 20° C. to 100°C. for 2 to 100 minutes. The reaction pressure is not particularlylimited but may be normal pressure. The solvent used in the reaction maybe selected from those compounds that can partly or completely dissolvethe titanium compound, the phosphorus compound, or a carbonyl-containingligand compound. Preferably, the solvent is selected from water,methanol, ethanol, ethylene glycol, propanediol, butanediol, benzene,and xylene.

(Invention Group II)

Organic polymer particles according to the Invention Group II can beprepared by emulsion polymerization, soap-free emulsion polymerization,seed emulsion polymerization, suspension polymerization, dispersionpolymerization, two-step expansion polymerization, or the like.

The organic polymer particles are preferably monodispersed in thepolyester. The monodispersed polymer can be obtained by melt-mixing theorganic polymer particles with a polymer. In particular, the organicpolymer particles are blended with water and/or an organic compoundhaving a boiling point of 200° C. or less to prepare a slurry, theslurry is added to a polyester, and the resulting mixture ismelt-kneaded in a vent-type molding machine while removing water and/orthe organic compound having a boiling point of 200° C. or less containedin the slurry.

Examples of the organic compound having a boiling point of 200° C. orless include alcohols such as methanol, ethanol, and ethylene glycol;hydrocarbons such as benzene and toluene; esters; ketones; and amines.From the standpoints of ease of handling and removal, water ispreferably used as a medium for the slurry.

The slurry of the organic polymer particles also contains an anionicsurfactant such as sodium dodecylbenzenesulfonate or sodium laurylsulfate, a nonion surfactant such as polyoxyethylene nonyl phenyl etheror polyethylene glycol monostearate, and the like.

The vent-type molding machine is a melt-molding machine having at leastone vent. The machine may be an extrusion molding machine or aninjection molding machine. At least one vent for removing water and/orthe organic compound having a boiling point of 200° C. or less should bemaintained under reduced pressure. The pressure is preferably reduced to13 KPa or less, more preferably 7 KPa or less, and most preferably 4 KPaor less.

The polyester films of the Invention Groups I to III contain thepolyester resin compositions of Invention Groups I to III, respectively.

The laminated polyester films of the Invention Groups I to III eachinclude a plurality of layers, at least one of which is composed of acorresponding polyester resin composition. The laminate structuresincluding layers composed of the polyester resin compositions of thepresent invention and layers composed of other polyester resincompositions can provide laminated films having all the characteristicsof these layers.

The polyester film of the present invention or the layer, which isincluded in the laminated polyester film of the present invention andcomposed of the polyester resin composition of the present invention,may be composed of the polyester resin composition alone or may becomposed of mixture of another polyester resin composition and 1 wt % ormore of the polyester resin composition of the present invention. Use ofsuch a mixture is also preferable from the standpoints of productivityand increasing the heat resistance.

(Invention Groups I and II)

The polyester resin compositions of the Invention Groups I and II eachcontain 30 ppm or less of antimony, as is described above. Even when afilm composed of such a polyester resin composition is laminated withfilms composed of a polyester containing more than 30 ppm of antimony ona weight basis, the amount of the antimony as a whole film can bereduced. Thus, it is preferable to use the polyester resin compositionin the laminated polyester film.

The laminated polyester films of the Invention Groups I and II aresuitable for magnetic recording medium applications. In such a case, atleast one surface of the recording medium is preferably a layer composedof the polyester resin composition of Invention Groups I and II. Byusing the polyester resin compositions of the Invention Groups I and II,a film having reduced numbers of coarse projections and flaws, excellentsurface quality, and high slidability can be obtained. Such a film canwithstand stringent film surface property requirements for magneticrecording media.

Next, a method for producing a polyester film by melt extrusion isexplained as an example of polyester film production processes.

A polyester resin composition is first prepared. The polyester resincomposition is preliminarily dried, if necessary, in hot blast or undervacuum, and fed to a single- or twin-shaft melt extruder.

In the extruder, the resin is melted by heating at a melting temperatureof higher and extruded at a uniform extrusion output by use of gear pumpand the like. Debris and degenerated resin are filtered off. The resinis then molded using a die, such as a T-die, and discharged.

In order to make a laminated film, for example, a technique oflaminating polyester resins fed from two or more extruders via differentchannels using a feed block equipped with rectangular laminating unit, astatic mixer, a multimanifold die, or the like may be used. Examples ofthe static mixer include a pipe mixer and a square mixer. From thestandpoint of uniform lamination, a square mixer is preferably used.

The sheet having a single or multilayered structure discharged from thedie is transferred onto a cooling unit, such as a casting drum, andcooled and solidified to obtain a casting film. When the sheet istransferred onto the cooling unit, it is preferable to applyelectrostatic force to the sheet using wire-type, tape-type,needle-type, or knife-type electrodes so that the sheet closely contactonto the cooling unit (electrostatic casting) to conduct rapid coolingand solidification.

The casting film is an unstretched film. The casting film may bebiaxially stretched depending on usage so as to prepare an orientedpolyester film. Biaxial stretching refers to stretching in longitudinaland transversal directions. The stretching may be sequentially orsimultaneously conducted in the two directions. Moreover, the film maybe stretched again in the longitudinal and/or transversal direction.

Here, “longitudinal stretching” refers to stretching that orients themolecules of the film in the longitudinal direction. For example, thefilm is longitudinally stretched by a difference in peripheral velocityof the rollers. The stretching may be conducted at one stage or at twoor more stages using a plurality of sets of rollers. The stretchingratio is preferably 2 to 15, preferably 2.5 to 7, and most preferably 5or less.

The surface of the film after longitudinal stretching may be coated, forexample, using a gravure coater, a metering bar coater, or the like toform an readily adhesive layer, a easy sliding layer, a particle layer,or the like. The coating may be performed between the longitudinalstretching and the transversal stretching, before or after thestretching, either in-line or off-line.

The “transversal stretching” refers to stretching that orients themolecules of the film in the transversal direction. For example, thefilm is transferred and stretched in the transversal direction in atenter while holding the two ends of the film with clips. The stretchingratio is preferably 2 to 10, and more preferably 5 or less.

Simultaneous biaxial stretching may be performed by simultaneouslystretching the film in the longitudinal and transversal directions whilebeing transferred with two ends being held with clips in a tenter.

The biaxially stretched film is preferably heated in a tenter at atemperature in the range of from the stretching temperature to themelting point so as to impart flatness and dimensional stability to thefilm. After heating, the film is slowly and uniformly cooled to roomtemperature, and wound. The heating temperature is preferably in therange of 120° C. to 240° C. from the standpoints of flatness anddimensional stability.

Since the polyester films of the Invention Groups I to III rarelycontain debris, the surface flatness thereof is high. The averageroughness Ra of the film surface is preferably in the range of 0.5 to 30nm, more preferably 1 to 20 nm, and most preferably 1 to 10 nm.

The polyester films and the laminated polyester films of the InventionGroups I to III have a low average roughness at the film surface and aresuitable as base films of magnetic recording media. In other words,magnetic recording media of the Invention Groups I to III include thelaminated polyester films or the polyester films of the Invention GroupsI to III, respectively. They are particularly suitable as magneticrecording media for computer data recording and digital video tapes thatrequire high recording densities.

(Invention Group III)

According to the Invention Group III, satisfactory hue (b value) can beyielded, debris can be reduced, and thermal stability during melting ishigh. Thus, the invention is suitable for fiber applications, packagingapplications, and optical material applications.

EXAMPLES

The present invention will now be described in further detail by way ofExamples below.

Measurement Methods Example 1 to 14 and Comparative Examples 1 to 5(1.1) Titanium Content, Phosphorus Content, Antimony Content, and theLike in the Polyester Resin Composition

Eight grams of a polyester resin composition was melted and molded toprepare a tabular sample. The intensity of fluorescent X-ray wasmeasured with a fluorescent X-ray analyzer, Model 3270 produced byRigaku Corporation. The observed value was compared with calibrationcurves preliminarily prepared using samples compositions of which wereknown, and the content of each element was determined by conversion.

(1.2) The Number of Coarse Debris in the Polyester Resin Composition(the Number Density of Titanium-Containing Particles)

Samples were prepared and measured by the following processes.

(1.2.1) Making Preparations

Polyester chips were washed with diluted hydrochloric acid, and thenwith purified water. On a slide glass, 0.2 mg of sample taken from thesepolyester chips was placed and melted at 280° C. A cover glass wasplaced thereon to sandwich the sample. The sample interposed between theslide glass and the cover glass was in a stretched state. The coverglass was then separated from the slide glass by sliding while beingheated to 280° C., and cooled at room temperature to obtain apreparation including the cover glass and a polymer thin film disposedon the cover glass. The polymer thin film on the preparation was incisedwith a sharp razor so as to form a grid of 10 rows×10 columns, i.e., atotal of 100 sections.

(1.2.2) Measurement of Particles with an Optical Microscope

An optical microscope, MetaloPlan, produced by Leitz Inc., was used. Themagnification of the object lens of the optical microscope was set to32×, dark field inspection was conducted, and the resulting image wasinput to a high-resolution monitor of an image analyzer. Since theobject lens had high magnification and the depth of focus was small,adjusting the focus to the top face allowed observation of the topsurface layer about 1 μm in depth.

The optical microscope was connected to a high-resolution personal imageanalysis system, PIAS-IV produced by Pias Co., Ltd. The observationmagnification was set to 1,560× on the monitor. A monochrome image wasinput, and the input image was binarized to conduct brightnessconversion. Here, the brightness was adjusted by adjusting the diaphragmof the optical microscope, for example, so that the average brightnesswas 183 (blank) when inspection was conducted without setting any sampleand that the brightness indicating the density level was 160 when asample was set.

From the binarized image, the diameters of equivalent circles of darkportions corresponding to the particles were determined as particlediameters. The number of the particles having a diameter of 1 μm or morewas counted, and the positions of such particles were identified usingthe grid.

(1.2.3) Confirming the Presence of Titanium

The polymer thin film on the preparation after the observation describedin (1.2.2) was subjected to plasma ashing and carbon deposition. Thesections of the grid in which the presence of the particles having adiameter of 1 μm or more was observed with the optical microscope wereinspected by SEM-XMA to determine the presence of titanium in theseparticles.

The number of particles having a diameter of 1 μm or more and containingtitanium in 0.02 mg of a polymer was defined as the particle numberdensity.

(1.3) Specific Volume Resistivity of the Melted Resin Composition

A resin composition was vacuum dried, placed in a test tube having aninner diameter of 50 mm, and melted at a film-making temperature (280°C.) in a nitrogen atmosphere. A pair of copper electrodes was insertedto the melted resin, and DC voltage was applied to the resin. Thespecific volume resistivity [ρ] of the melted resin was determined bythe following equation (unit: Ω·cm):

[ρ]=(V×S)/(I×D)

where V is an applied voltage (V), S is the area of electrodes (cm²), Iis a current value (A), and D is the distance between the electrodes(cm).

(4) Cast Surface Quality

At least 10 m² of the cast sheet was exposed to light, and the reflectedlight was observed to determine the presence of surface irregularities,such as craters. The sheet was evaluated good (◯) when no irregularitywas observed, fair (Δ) when irregularities were observed in part of thesurface or were shallow, i.e., having a depth of less than 0.1 μm, suchthat the irregularities would vanish by stretching, and poor (x) whenirregularities were observed over the entire surface.

(1.5) Surface Roughness Ra

Surface roughness was measured according to Japanese IndustrialStandards (JIS) B-0601.

Measurement was conducted with a precision thin-film step analyzer,ET-10 produced by Kosaka Laboratory, Ltd., equipped with a stylus havinga tip radius of 0.5 μm, at a stylus force of 5 mg, sampling length of 1mm, and a cutoff value of 0.08 mm.

(1.6) Drop-Out Characteristics

Using a commercially available Hi-8 VTR, a 4.4 MHz signal was suppliedfrom a TV sample signal generator, and the number of dropouts in whichthe attenuation and the length of the regenerative signal was −16 dB ormore and 15 microseconds or more, respectively, was counted with adrop-out counter. A cycle of three-minutes of playing/rewinding at 25°C. and 65% RH was repeated 100 times, and then the number of dropoutsoccurred during the three minutes of playing was converted to a valueper minute. The drop-out characteristics were evaluated as follows:

0 to 15/min: Excellent (pass)

16 to 30/min: Good (pass)

31 or more/min: Not good (fail)

Examples 15 to 19, Reference Examples 1 to 3, and Comparative Examples 6and 7 (2.1) Titanium Content, Phosphorus Content, and Antimony Contentin the Polyester

The contents were determined as in (1.1) above.

(2.2) Average Particle Diameter of Organic Polymer Particles

Determination was conducted by dynamic light scattering using PAR-IIIproduced by Otsuka Electronics Co., Ltd.

(2.3) The Ratio of the Number of the Coarse Particles Having a Diameterat Least Twice the Average Diameter in the Organic Polymer Particles(2.3.1) Measurement Using a Slurry

A slurry containing 20 wt % of organic polymer particles in water asmedium was diluted 1,000-fold with deionized water, and the number ofthe coarse particles having a diameter at least twice the averagediameter was counted using FPIA-2100 produced by Sysmex Corporation. Thetotal weight of the particles were calculated based on the weight of thesample used for measurement and divided by the density of the organicpolymer particles (about 1 g/cm³ for each example) to obtain the totalnumber of the particles. The number of the coarse particles was dividedby the total number of the particles to determine the ratio of thecoarse particles having a diameter at least twice the average diameterin the organic polymer particles.

(2.3.2) Measurement Using a Resin Composition

To 0.1 g of a resin composition containing organic polymer particles, 10mL of orthochlorophenol was added and dissolved at 100° C. for 30minutes under stirring. The resulting solution was left to stand at roomtemperature until the solution was cooled to normal temperature.Subsequently, the solution was diluted 5 fold or more indichloromethane, and the number of coarse particles having a diameter atleast twice the average diameter was determined with FPIA-2100 producedby Sysmex Corporation. Subsequently, the same calculation was conductedas in (2.3.1).

(2.4) Intrinsic Viscosity of the Polymer ([η] (dL/g))

The intrinsic viscosity of the polymer was measured at 25° C. usingorthochlorophenol as a solvent.

(2.5) Contamination of Casting Drums and Preheat Rollers

Prior to film making, a casting drum, preheat rollers, and theirperipheral areas were thoroughly cleaned. The state of contamination 48hours after initiation of the film-making was observed with human eyes.The rating “⊙” was given when the same cleaned state was maintained asbefore the film making, the rating “◯” was given when no contaminationwas easily recognizable, the rating “Δ” was given when slightcontamination was observed but operation was continuable, and the rating“x” was given when thick layers of contaminants were deposited andcleaning or replacement were necessary.

(2.6) Number of Coarse Projections in the Film Surface

Two films of the same EXAMPLE or COMPARATIVE EXAMPLE were superimposedon each other so that 100 cm² of the measuring face came into contactwith each other. The two films were closely contact onto each other byelectrostatic force by applying a voltage of 5.4 kV. The coarseprojections were detected from Newton's rings generated by interferenceof light with the coarse projections between the two films. The lightsource was a halogen lamp equipped with a 564-nm band pass filter.Newton's rings indicate the height of the coarse projections. The heightof a coarse projection showing two or more rings is at least 0.5 μmlarger by reason of the wavelength of the light.

(2.7) Flaws in Film Surface

A biaxially stretched film 48 hours after initiation of continuous filmmaking was examined as a sample of 165 cm in width and 20 m in lengthsubjected to transversal stretching and heating in a tenter. The filmwas visually examined under transmitted light, and the number of flawsfound in the surface was counted. The rating poor (“x”) was given whenthe number of flaws was 10 or more and the film cannot withstandpractical use; the rating fair (“Δ”) was given when the number of flawswas 3 to 9 but the film was still usable despite the low surfacequality; the rating good (“◯”) was given when the number of flaws was 1to 2 and the surface quality was high; and the rating excellent (“⊙”)was given when no flaw was found.

Examples 20 to 30 and Comparative Examples 8 to 12 (3.1) Content ofCarboxyl Terminal Groups (COOH) in the Polyester

The content of carboxyl terminal groups was determined by the methodproposed by Maurice and others, set forth in Anal. Chim. Acta, 22, p.363 (1960).

(3.2) Intrinsic Viscosity of the Polymer ([η] (dL/g))

The intrinsic viscosity was determined at 25° C. in o-chlorophenol as asolvent.

(3.3) The Titanium Content, Phosphorus Content, and Antimony Content inthe Polyester

The contents were determined as in (1.1) above.

(3.4) The Content of an Alkaline Metal Element in the Polyester ResinComposition

The alkaline metal content was determined by flame atomic absorptionspectrometry. An 8 g sample of a polyester resin composition wasprepared and air-acetylene flame was used. The light source was a hollowcathode lamp. The absorption at spectrum corresponding to each elementis measured with a polarized Zeeman-effect atomic absorptionspectrometer, model 180-80 produced by Hitachi Ltd. The observedabsorption was compared with calibration curves prepared in advance todetermine the content of each element by conversion.

(3.5) The Number of Debris

Polyester chips were washed with diluted hydrochloric acid and then withpurified water. A 10 mg sample was taken from the polyester chips andmelted on a preparation heated to 260° C. Among about 500 fields of viewthat can be observed in the preparation, 10 fields of view wereobserved, and the number of debris having a maximum diameter of 1 μm ormore was counted.

(3.6) Melt Specific Resistivity

A spacer composed of Teflon (trademark) was interposed between twocopper plates functioning as electrodes. The electrodes each had an areaof 22 cm², and the distance between the copper plates was 9 mm. Theelectrodes were immersed in a polymer melted at 290° C., and a voltageof 5,000 V was applied between the electrodes to determine theresistance from the current value.

(3.7) Thermal Stability of the Resin Composition (% BB)

In a test tube, 8 g of a resin composition was placed and heated in anitrogen atmosphere at a pressure of 0.1 MPa at 300° C. for 10 minutes(t₀) and 6 hours (t) to determine the intrinsic viscosities [η]_(t0) and[η]_(t). The thermal stability was calculated from the followingequation:

% BB _(t)=(1/[η]_(t) ^((1/0.75))−1/[η]_(t0) ^((1/0.75)))

(3.8) Hue of the Resin Composition

Resin composition chips were analyzed with a colorimeter (SM colorcomputer, SM-3CH) produced by Suga Test Instruments Co., Ltd., at ameasuring geometry of 45°/0° using illuminant C as the light source in a2° field of view to determine Hunter values for L, a, and b.

(3.9) Castability by Electro-Pinning

A DC voltage of 6 kV was applied between the electrode installed abovethe melt-extruded film and a rotating cooling unit while the castingrate was increased. The castability was determined based on the castingrate at which the electro-pinning became nonuniform according to thefollowing standards (rating B or higher was assumed as “pass”):

60 m/min<S50 to 60 m/min A40 to 50 m/min B30 to 40 m/min C<30 m/min D

(3.9) Numbers H1 and H2 of Coarse Projections in the Film

The numbers were determined by observation of Newton's rings as in (2.6)above. The number of coarse projections that yielded a single Newtonring was defined as H1, and the number of coarse projections thatyielded two or more Newton rings was defined as H2.

Note that when determination in the above-described measurement area isdifficult, the measurement area may be adequately changed, and thenumber may then be converted to a 100-cm² equivalent. (For example, themeasurement area may be changed to 1 cm², and the results obtained byinspecting 50 fields of view may be converted to a 100-cm² equivalent.)

If the above-mentioned technique is difficult, the number of projectionshaving a height of 0.28 μm or more and the number of projections havinga height of 0.56 μm or more may be counted using a 3D roughness meter(SE-3AK, produced by Kosaka Laboratory, Ltd.; the measurement may becarried out 50 times while scanning the film in the transversaldirection under the following conditions: stylus tip radius: 2 μm;stylus load: 0.07 g; measurement area: 0.5 mm (width)×15 mm (length),(pitch: 0.1 mm); and cutoff value: 0.08 mm), and then the results may beconverted to 100-cm² equivalents. If necessary, a known device forcounting the number of projections in the film surface, such as anatomic force microscope (AFM) or a four-detector SEM, may be used incombination.

[Catalyst A: Titanium Citrate Chelate Compound]

In a 3 L flask equipped with a stirrer, a condenser, and a thermometer,hot water (371 g) was charged, and citric acid monohydrate (532 g, 2.52mol) was dissolved therein. While stirring the solution, titaniumtetraisopropoxide (288 g, 1.00 mol) was gradually added to the solutionwith a dropping funnel. The resulting mixture was heated for 1 hour andrefluxed to yield a clouded solution. Subsequently, an isopropanol/watermixture was distilled away under reduced pressure. The resulting liquidincorporating the products was cooled to a temperature lower than 70°C., and a 32 wt % aqueous solution of NaOH (380 g, 3.04 mol) wasgradually added to this liquid while stirring the liquid using adropping funnel. The products were separated by filtration, combinedwith ethylene glycol (504 g, 80 mol), and heated under reduced pressureto remove isopropanol/water. A slightly clouded pale yellow product (Ticontent: 3.85 wt %) was obtained as a result. The product was diluted inethylene glycol to prepare an ethylene glycol solution containing 1 wt %of a titanium compound. This titanium citrate chelate compound was usedas a catalyst A.

[Catalyst B: Titanium Lactate Chelate Compound]

To a 2 L flask equipped with a stirrer, a condenser, and a thermometerand charged with titanium tetraisopropoxide (285 g, 1.00 mol), ethyleneglycol (218 g, 3.51 mol) was gradually added using a dropping funnelunder stirring. The speed of addition is adjusted so that the content ofthe flask was heated to about 50° C. by the reaction heat. The reactionmixture was stirred for 15 minutes, and an 85 wt % aqueous solution ofammonium lactate (252 g, 2.00 mol) was fed to the reaction flask. Atransparent pale yellow product (Ti content: 6.54 wt %) was obtained asa result. This product was diluted in ethylene glycol to prepare anethylene glycol solution containing 1 wt % of a titanium compound. Thistitanium lactate chelate compound was used as a catalyst B.

[Catalyst C: Titanium Alkoxide Compound]

To a 2 L flask equipped with a stirrer, a condenser, and a thermometerand charged with titanium tetraisopropoxide (285 g, 1.00 mol), ethyleneglycol (496 gm 8.00 mol) was added using a dropping funnel understirring. The speed of addition was adjusted so that the contents of theflask were heated to about 50° C. by the reaction heat. To the reactionflask, a 32 wt % aqueous solution of NaOH (125 g, 1.00 mol) wasgradually fed using a dropping funnel to obtain a transparent yellowliquid (Ti content: 4.44 wt %). The liquid was diluted in ethyleneglycol to prepare an ethylene glycol solution containing 1 wt % of atitanium compound. This titanium alkoxide compound was used as acatalyst C.

Example 1 Ethylene Glycol Slurry of Colloidal Silica Particles

To 40 parts by weight of ethyl alcohol, 4 parts by weight of saturatedammonia water was added, and 4 parts by weight of tetrapentylsilicon wasadded under stirring to prepare colloidal silica having an averageparticle diameter of 0.1 μm. Subsequently, 100 parts by weight ofethylene glycol was added, and the mixture was heated to distill awayethanol and water. Ethylene glycol slurry of colloidal silica wasobtained as a result.

(Preparation of Polyethylene Terephthalate Resin Composition)

Into an esterification reactor preliminarily charged with about 120parts by weight of bis(hydroxyethyl) terephthalate and kept at 250° C.,an ethylene glycol slurry of terephthalic acid, the slurry containing100 parts by weight of high-purity terephthalic acid and 43 parts byweight of ethylene glycol, was continuously fed over four hours. Upontermination of the feeding, esterification reaction was continued for 1hour while distilling away water. Subsequently, 120 parts by weight ofesterification reaction products were transferred to a polycondensationreactor.

Into the polycondensation reactor charged with the esterificationreaction products, 0.01 part by weight of ethyl diethylphosphonoacetatewas fed, and then 0.03 part by weight of magnesium acetate tetrahydrateand the catalyst C described above in an amount of 5 ppm in terms oftitanium were added. The ethylene glycol slurry of colloidal silicadescribed above was added so that the particle density in the polymerwas 0.1%.

Subsequently, while stirring the resulting lower polymer, the reactionsystem was gradually heated from 250° C. to 285° C. while the pressurewas reduced to 100 Pa. When a predetermined stirring torque was reached,the reaction system was nitrogen-purged to return the pressure tonormal, thereby terminating the polycondensation reaction.

The resulting resin composition was discharged in strands into coldwater. The strands were immediately cut to prepare pellets.

The specific volume resistivity of the pellets when melted (280° C.) was80 MΩ·cm (8×10⁷ Ω·cm).

(Preparation of Polyester Films)

The pellets of the polyethylene terephthalate resin compositiondescribed above were dried in a vacuum drier and fed to an extruder.

In the extruder, the polyethylene terephthalate resin composition wasmelted at 280° C., sent through a gear pump and a filter, and fed to aT-die to prepare a sheet. The sheet was rapidly cooled and solidified ona casting drum having a surface temperature maintained at 20° C. whileapplying electrostatic charge with wire electrodes.

This cast film was heated with rollers having a surface temperature of90° C., and stretched 3.0 fold in the longitudinal direction.

Next, the film was introduced into a tenter, preheated with hot blast at100° C., and stretched 3.3 fold in the transversal direction. In thesame tenter, the film was heated by hot blast at 200° C., slowly cooledto room temperature, and wound. The thickness of the resulting film was10 μm.

(Preparation of a Magnetic Recording Medium)

On a surface of the film, a magnetic coating composition and a backcoating composition, compositions of which are described below, wereapplied.

(Magnetic coating composition) Ferrous metal ferromagnetic powder 100parts by weight A vinyl chloride/vinyl acetate copolymer 10 parts byweight A polyurethane elastomer 10 parts by weight Polyisocyanate 5parts by weight Lecithin 1 part by weight Methyl ethyl ketone 75 partsby weight Methyl isobutyl ketone 75 parts by weight Toluene 75 parts byweight Carbon black 2 parts by weight Lauric acid 1.5 parts by weight

(Back coating composition) Carbon black 100 parts by weight Polyesterpolyurethane resin 100 parts by weight Methyl ethyl ketone 500 parts byweight Toluene 500 parts by weightThe film was subjected to calendering using a small calendering machine(styrol/nylon roll) for testing, at 70° C. and a linear load of 2,000N/cm. Subsequently, the compositions were cured for 48 hours at 70° C.The original tape was cut to a width of 8 mm and assembled into acassette to prepare a cassette tape.

Examples 2 to 4

A polyethylene terephthalate resin composition, a film, and a magnetictape were prepared as in EXAMPLE 1 except that the type and the amountof titanium catalyst, the type and the amount of the alkaline earthmetal compound (in EXAMPLE 2, magnesium acetate tetrahydrate as inEXAMPLE 1, and in EXAMPLE 4, calcium acetate monohydrate were used), andthe amount of the ethyl diethylphosphonoacetate were changed.

Comparative Example 1

A polyester resin, a film, and a magnetic tape were prepared as inEXAMPLE 1, except that the amount of the titanium catalyst added waschanged to 60 ppm on a weight basis in terms of titanium.

Because of the titanium content exceeding 50 ppm, large amounts ofdebris were contained in the resin, and the magnetic tape frequentlysuffered from drop-outs.

Comparative Example 2

Preparation of Polyethylene Terephthalate Resin composition etc., wasattempted as in EXAMPLE 1 but with 0.2 ppm of a titanium catalyst on aweight basis in terms of titanium. However, a resin having asufficiently high degree of polymerization for forming films was notobtained.

Comparative Example 3

A polyethylene terephthalate resin composition was prepared as inEXAMPLE 1 except that antimony trioxide was used as the polymerizationcatalyst instead of the catalyst C, in an amount of 200 ppm on a weightbasis in terms of antimony and that magnesium acetate tetrahydrate wasnot used.

An attempt was made to make a film as in EXAMPLE 1 using this resincomposition; however, the castability was poor, and crater-shaped flawswere found in the film surface. This film was not sufficient to beprocessed into a magnetic tape.

Example 5 Resin Composition Prepared in the Presence of a TitaniumCatalyst

A polyethylene terephthalate resin composition was prepared as inEXAMPLE 2 but without adding any colloidal silica.

(Resin Composition Prepared in the Presence of a Antimony Catalyst)

The polyester resin prepared in COMPARATIVE 3 was used.

(Preparation of a Laminated Polyester Film)

The two polyethylene terephthalate resin compositions above wereindependently fed to separate extruders, extruded, and laminated to forma two-layered composite using a feed block. The composite was fed to aT-die and formed into a sheet. The sheet was rapidly cooled andsolidified on a casting drum having a surface temperature maintained at20° C. while applying electrostatic charge by wire electrodes.

The cast film was heated with rollers having a surface temperature of90° C., and stretched 3.0 fold in the longitudinal direction.

Subsequently, the film was introduced into a tenter, preheated in a hotblast at 100° C., and stretched 3.3 fold in the transversal direction.In the same tenter, the film was heated in a hot blast at 200° C.,slowly cooled to room temperature, and wound. The lamination ratio ofthe film was 90 wt % the resin prepared in the presence of the titaniumcatalyst and 10 wt % the resin prepared in the presence of the antimonycatalyst.

The laminated film was processed into a magnetic tape, as in EXAMPLE 1,by applying magnetic compositions on a surface composed of the resinprepared in the presence of the titanium catalyst.

Example 6

A polyester resin composition, a film, and a magnetic tape were preparedas in EXAMPLE 1 except that the phosphorus compound was changed fromethyl diethylphosphonoacetate to trimethylphosphoric acid in an amountof 10 ppm on a weight basis in terms of phosphorus.

Example 7

A polyester resin composition, a film, and a magnetic tape were preparedas in EXAMPLE 1 except that the phosphorus compound was changed fromethyl diethylphosphonoacetate to phosphoric acid in an amount of 10 ppmon a weight basis in terms of phosphorus.

Example 8

A polyester resin composition, a film, and a magnetic tape were preparedas in EXAMPLE 1 except that the amount of the catalyst C was changed to35 ppm on a weight basis in terms of titanium.

Examples 9 to 12

A polyester resin composition, a film, and a magnetic tape were preparedas in EXAMPLE 3 except that the amount of the magnesium acetatetetrahydrate added before the polycondensation was changed respectively.

Examples 13 and 14 and Comparative Example 4

A polyester resin composition, a film, and a magnetic tape were preparedas in EXAMPLE 2 except that the amount of ethyl diethylphosphonoacetateadded was changed respectively.

Comparative Example 5

An attempt was made to prepare a polyester resin as in EXAMPLE 2 exceptthat the amount of the ethyl diethylphosphonoacetate added was changed.However, the polymerization rate was excessively low, and the resultingresin did not have a sufficient degree of polymerization for filmproduction.

The results of EXAMPLES 1 to 14 and COMPARATIVE EXAMPLES 1 to 5 areshown in Tables 1-1 and 1-2.

Note that in these tables, the content of each element in EXAMPLE 5 isrelative to the entirety of the film. Moreover, in EXAMPLE 5, thesurface composed of the resin composition prepared in the presence ofthe titanium catalyst was evaluated as to its film properties.

TABLE 1-1 Composition of polyester resin Alkaline Ti Type of earth Pcontent Ti content content Sb content (ppm) catalyst (type/ppm) (ppm)(ppm) EXAMPLE 1 5 C Mg/30 10 0 EXAMPLE 2 15 B Mg/30 10 0 EXAMPLE 3 5 ANone 10 0 EXAMPLE 4 2 A Ca/100 35 0 EXAMPLE 5 13.5 B Mg/27 10 20 EXAMPLE6 5 C Mg/30 10 0 EXAMPLE 7 5 C Mg/30 10 0 EXAMPLE 8 35 C Mg/30 10 0EXAMPLE 9 5 A Mg/15 10 0 EXAMPLE 10 5 A Mg/60 10 0 EXAMPLE 11 5 A Mg/7010 0 EXAMPLE 12 5 A Mg/100 10 0 EXAMPLE 13 15 B Mg/30 1 0 EXAMPLE 14 15B Mg/30 80 0 COMPARATIVE 60 C Mg/30 10 0 EXAMPLE 1 COMPARATIVE 0.2 CMg/30 10 0 EXAMPLE 2 COMPARATIVE 0 — None 10 200 EXAMPLE 3 COMPARATIVE15 B Mg/30 0 0 EXAMPLE 4 COMPARATIVE 15 B Mg/30 120 0 EXAMPLE 5

TABLE 1-2 Polyester resin properties Film properties Specific No. ofNumber volume particles of resistivity (No./ drop-outs when melted 0.02Ra (pass or (MΩ · cm) mg) Castability (nm) fail/No.) EXAMPLE 1 80 3 ◯ 6Pass/3 EXAMPLE 2 50 50 ◯ 12 Pass/12 EXAMPLE 3 500 7 Δ 5 Pass/6 EXAMPLE 440 2 ◯ 10 Pass/10 EXAMPLE 5 — — ◯ 10 Pass/10 EXAMPLE 6 85 15 ◯ 13Pass/16 EXAMPLE 7 90 30 ◯ 14 Pass/18 EXAMPLE 8 75 90 ◯ 17 Pass/25EXAMPLE 9 250 10 ◯ 12 Pass/10 EXAMPLE 10 40 15 ◯ 13 Pass/15 EXAMPLE 1130 55 ◯ 15 Pass/19 EXAMPLE 12 10 80 ◯ 16 Pass/24 EXAMPLE 13 30 85 ◯ 17Pass/26 EXAMPLE 14 800 92 Δ 17 Pass/28 COMPARATIVE 60 260 ◯ 20 Fail/50EXAMPLE 1 COMPARATIVE — — — — — EXAMPLE 2 COMPARATIVE 1000 0 X — —EXAMPLE 3 COMPARATIVE 30 110 ◯ 20 Fail/35 EXAMPLE 4 COMPARATIVE — — — —— EXAMPLE 5

Example 15 Preparation of a Polyethylene Terephthalate Resin Composition

Into an esterification reactor preliminarily charged with about 120parts by weight of bis(hydroxyethyl) terephthalate and kept at 250° C.and a pressure of 1.2×10⁵ Pa, an ethylene glycol slurry of terephthalicacid, the slurry containing 100 parts by weight of high-purityterephthalic acid and 43 parts by weight of ethylene glycol, wascontinuously fed over four hours. Upon termination of the feeding,esterification reaction was continued for 1 hour. Then, 120 parts byweight of the esterification reaction products were transferred to apolycondensation reactor.

Into the polycondensation reactor charged with the esterificationreaction products, 10 ppm of an ethylene glycol solution oftriethylphosphonoacetate in terms of phosphorus was fed. Ten minuteslater, an ethylene glycol solution of magnesium acetate tetrahydrate inan amount of 39 ppm in terms of magnesium relative to a polymer to beobtained and a 1 wt % ethylene glycol solution of titanium citratechelate compound (catalyst A) in an amount of 5 ppm in terms of titaniumrelative to the polymer to be obtained were added to the reactionsystem.

Subsequently, while stirring the resulting lower polymer at 30 rpm, thereaction system was gradually heated from 250° C. to 285° C. while thepressure was reduced to 40 Pa. The time taken until the finaltemperature and final pressure were reached in heating and pressurereduction was set to 60 minutes. When a predetermined stirring torquewas reached, the reaction system was nitrogen-purged to return thepressure to normal, thereby terminating the polycondensation reaction.The time taken from the initiation of pressure reduction to reaching ofthe target stirring torque was 3 hours.

The resulting resin composition was discharged in strands into coldwater. The strands were immediately cut to prepare pellets.

The intrinsic viscosity of the resulting polymer was 0.65. The contentof titanium derived from the titanium catalyst in the resin compositionwas 5 ppm, the phosphorus content was 10 ppm, and the antimony contentwas 0 ppm.

(Preparation and Addition of Organic Polymer Particles)

Organic polymer particles were prepared by a seed emulsionpolymerization technique, in which seed particles having a significantlynarrow particle size distribution were obtained by conducting seedpolymerization in multiple stages. Using these seed particles, seedemulsion polymerization was conducted. Subsequently, circulationfiltration was conducted using a filter, which had an absolutefiltration accuracy of twice the average particle diameter and wasproduced by Pall Corporation, for 20 passes to prepare an aqueous slurryof a vinylbenzene-divinylbenzene copolymer organic polymer particleshaving an average particle diameter of 0.3 μm, a degree of cross-linkingof 80%, and a ratio of coarse particles of 0.001%.

The above-described pellets were melted in a vent-type twin-shaftextruder, and the organic polymer particles were added thereto so thatthe content of the organic polymer particles in the resin composition tobe obtained becomes 2 wt %.

After the organic polymer particles were added, the resin compositionwas melt-extruded at a resin composition temperature of 280° C. whilemaintaining the vent port of the extruder under a vacuum of 1 KPa. Theextruded composition was cut to prepare pellets of the polyethyleneterephthalate resin composition containing the organic polymerparticles. The intrinsic viscosity of the polymer was 0.60.

(Preparation of a Laminated Polyester Film)

Twenty parts by weight of a resin composition containing the organicpolymer particles described above and 80 parts by weight of a resincomposition to which no organic polymer particle was added were driedseparately, and fed to separate single-shaft extruders. The compositionswere combined using a T-die to prepare a two-layer structure in whichthe ratio of the two layers was 5:1. The two-layer structure wasmelt-extruded at 290° C. to prepare a sheet. The sheet was biaxiallystretched at a stretching temperature of 120° C. to prepare a laminatedfilm having a thickness of 6 μm. The properties of this laminated filmwere investigated. The film showed satisfactory surface quality.

Example 16

A polyester resin composition and a film were prepared as in EXAMPLE 15except for the following. In preparing the polyethylene terephthalateresin composition, 95 parts by weight of high-purity terephthalic acidand 5 parts by weight of 5-sodium sulfoisophthalic acid were usedinstead of 100 parts by weight of high-purity terephthalic acid; theamount of the catalyst A added was changed to 10 ppm in terms oftitanium; and the organic polymer particles were surface-treated byadding 1 wt % of polyvinyl pyrrolidone relative to the organic polymerparticles to an aqueous slurry of the organic polymer particles andstirring the resulting mixture for 3 hours at normal temperature.

Example 17

A polyester resin composition and a film were obtained as in EXAMPLE 15except that 0.5 μm silicone particles were used as the organic polymerparticles.

Example 18

A polyester resin composition and a film were prepared as in EXAMPLE 15except that the catalyst B was used instead of the catalyst A, theamount of triethylphosphonoacetate added was changed to 20 ppm in termsof phosphorus, the average particle diameter ofvinylbenzene-divinylbenzene organic polymer particles was changed to 0.8μm, and the ratio of the coarse particles was changed to 0.005%.

Example 19

A polyester resin composition and a film were obtained as in EXAMPLE 15,except that the catalyst C was used instead of the catalyst A, theamount of triethylphosphonoacetate added was changed to 40 ppm in termsof phosphorus, the average particle diameter ofvinylbenzene-divinylbenzene organic polymer particles was changed to 2.7μm, and the ratio of the coarse particles were changed to 0.01%.

Comparative Example 6

A polyester resin composition and a film were obtained as in EXAMPLE 15,except that antimony trioxide in an amount of 200 ppm relative to theresulting polymer in terms of antimony was added instead of the catalystA. Although the polymerization reactivity was satisfactory,contamination of the casting drum and preheat rollers occurred duringfilm-making. Moreover, the resulting film had significantly increasedflaws and coarse projections in its surface.

Reference Example 1

A polyester resin composition and a film were obtained as in EXAMPLE 15,except that the ratio of the coarse particles ofvinylbenzene-divinylbenzene was changed to 0.02%. The flaws in the filmsurface increased; in particular, the number of coarse projections wasas high as 300/100 cm².

Reference Example 2

A polyester resin composition and a film were obtained as in EXAMPLE 15,except that the amount of the triethylphosphonoacetate was changed to 20ppm in terms of phosphorus, the average particle diameter of thevinylbenzene-divinylbenzene organic polymer particles was changed to 5μm, and the ratio of the coarse particles was 0.005%. The flaws in thefilm surface increased; in particular, the number of coarse projectionswas as high as 250/100 cm².

Reference Example 3

An attempt was made to prepare a polyester resin composition as inEXAMPLE 15 but with 60 ppm of triethylphosphonoacetate in terms ofphosphorus. However, the particles could not be mixed, and the resultingproduct did not have a degree of polymerization suitable for filmproduction.

Comparative Example 7

A polyester resin composition and a film were prepared as in EXAMPLE 15except that the amount of the catalyst A added was changed to 100 ppm interms of titanium. The number of coarse projections in the filmincreased to 200 per square centimeter.

The results of EXAMPLES 15 to 19, REFERENCE EXAMPLES 1 to 3, andCOMPARATIVE EXAMPLES 6 and 7 are shown in Tables 2-1 to 2-3.

TABLE 2-1 Composition of polyester resin Type of Ti content P content Sbcontent catalyst (ppm) (ppm) (ppm) EXAMPLE 15 A 5 10 0 EXAMPLE 16 A 1010 0 EXAMPLE 17 A 5 10 0 EXAMPLE 18 B 5 20 0 EXAMPLE 19 C 5 40 0COMPARATIVE — 0 10 200 EXAMPLE 6 COMPARATIVE A 100 10 0 EXAMPLE 7REFERENCE A 5 10 0 EXAMPLE 1 REFERENCE A 5 20 0 EXAMPLE 2 REFERENCE A 560 0 EXAMPLE 3

TABLE 2-2 Properties of organic polymer particles contained in thepolyester resin composition Type of Ratio of organic coarse polymerAverage particles particles diameter (μm) (%) EXAMPLE 15 Vinylbenzene-0.3 0.001 divinylbenzene EXAMPLE 16 Vinylbenzene- 0.3 0.001divinylbenzene EXAMPLE 17 Silicone 0.5 0.001 EXAMPLE 18 Vinylbenzene-0.8 0.005 divinylbenzene EXAMPLE 19 Vinylbenzene- 2.7 0.010divinylbenzene COMPARATIVE Vinylbenzene- 0.3 0.001 EXAMPLE 6divinylbenzene COMPARATIVE Vinylbenzene- 0.3 0.001 EXAMPLE 7divinylbenzene REFERENCE Vinylbenzene- 0.3 0.020 EXAMPLE 1divinylbenzene REFERENCE Vinylbenzene- 5.0 0.005 EXAMPLE 2divinylbenzene REFERENCE — — — EXAMPLE 3

TABLE 2-3 Properties of film Contamination of casting Coarse drum andprojections in preheat Flaws in film film surface rollers surface(No./100 cm²) EXAMPLE 15 ⊙ ⊙ 20 EXAMPLE 16 ⊙ ◯ 30 EXAMPLE 17 ⊙ ⊙ 30EXAMPLE 18 ◯ ⊙ 50 EXAMPLE 19 ◯ ◯ 80 COMPARATIVE Δ X 200 EXAMPLE 6COMPARATIVE Δ Δ 200 EXAMPLE 7 REFERENCE Δ Δ 300 EXAMPLE 1 REFERENCE Δ X250 EXAMPLE 2 REFERENCE — — — EXAMPLE 3

Example 20 Catalyst Preparation

To 94.95 parts by weight of ethylene glycol, 0.05 part by weight of thecompound represented by the formula D above was added as a ligandcompound β and dissolved by heating at 150° C. for 30 minutes. To theresulting ethylene glycol solution, 5 parts by weight of an isopropylalcohol solution of titanium acetylacetonate as the compound α (thedensity of the solution was 10 wt % in terms of titanium) was added anddissolved at 150° C. for 1 hour to prepare a catalyst slurry. Thetitanium content in the slurry was 5,000 ppm.

(Preparation of a Polyester Resin Composition)

Using the esterification reaction products of 86 parts by weight ofterephthalic acid and 39 parts by weight of ethylene glycol as areservoir, 86 parts by weight of terephthalic acid and 39 parts byweight of ethylene glycol were added to this reservoir, and theesterification was continued at 250° C. Upon reaching the reaction rateof 97% or higher, the esterification reaction products corresponding to86 parts by weight of terephthalic acid were transferred to apolycondensation can, and 0.1 part by weight of the above-describedcatalyst and 0.004 part by weight of dimethyl methylphosphonate were fedto this can. The resulting mixture was transferred to a polycondensationreactor. The reaction system was gradually vacuumed while heating, andpolycondensation was conducted under a reduced pressure of 133 Pa at285° C. for 3 hours according to a conventional technique under stirringat a constant rate. A polyester composition I having an intrinsicviscosity of 0.630 was obtained as a result.

Examples 21 to 23

Polyester resin compositions II, III, and IV having intrinsicviscosities of 0.64, 0.63, and 0.64, respectively, and catalysts wereprepared as in EXAMPLE 20 but with changes set forth in Table 3-1regarding the catalyst preparation and the amount of the catalyst added.

Example 24 Catalyst Preparation

To 94.975 parts by weight of ethylene glycol, 0.025 part by weight ofthe compound represented by the formula D above was added as a ligandcompound β and dissolved by heating at 150° C. for 30 minutes. To thisethylene glycol solution, 5 parts by weight of an isopropyl alcoholsolution of tetrabutyl titanate as the compound α (the density of thesolution being 10 wt % in terms of titanium) was added and dissolved at150° C. for 1 hour to prepare a catalyst slurry. The titanium content inthe slurry was 5,000 ppm.

(Preparation of a Polyester Resin Composition)

A polyester resin composition V having an intrinsic viscosity of 0.630was prepared as in EXAMPLE 20 except that the above-described slurry wasadded as a catalyst in an amount of 0.1 part by weight and that 0.005part by weight of dipropynyl methylphosphonate was added instead of0.004 part by weight of dimethyl methylphosphonate.

Example 25 Catalyst Preparation

To 94.7 parts by weight of ethylene glycol, 0.3 part by weight of thecompound represented by formula D was added as a ligand compound β at25° C. To this ethylene glycol solution, 5 parts by weight of anisopropyl alcohol solution of titanium citrate chelate as the compound awas added (the density of the solution being 10 wt % in terms oftitanium), and the mixture was mixed at normal temperature to obtain acatalyst slurry. The titanium content in the slurry was 5,000 ppm.

(Preparation of Polyester)

A polyester resin composition VI having an intrinsic viscosity of 0.63was obtained as in EXAMPLE 20, except that 0.16 part by weight of theabove-described slurry was used as the catalyst, that 0.004 part byweight of ethyl diethylphosphonoacetate was used instead of 0.004 partby weight of dimethyl methylphosphonate, and that 0.03 part by weight ofmagnesium acetate tetrahydrate was added.

Example 26

A polyester resin composition VII having an intrinsic viscosity of 0.64and a catalyst were prepared as in EXAMPLE 25 except that an aqueoussolution of ammonium titaniumperoxocitrate was used as the compound α.

Comparative Example 8

Using the esterification reaction products of 86 parts by weight ofterephthalic acid and 39 parts by weight of ethylene glycol as areservoir, 86 parts by weight of terephthalic acid and 39 parts byweight of ethylene glycol were added to this reservoir, and theesterification was continued at 250° C. Upon reaching the reaction rateof 97% or higher, the esterification reaction products corresponding to86 parts by weight of terephthalic acid were transferred to apolycondensation can, and 0.0035 part by weight of tetrabutyl titanateand 0.005 part by weight of dipropyl methylphosphonate were added. Theresulting mixture was transferred to a polycondensation reactor. Thereaction system was gradually vacuum while heating, and polycondensationwas conducted for 3 hours under a vacuum of 133 Pa at 285° C. by aconventional technique under stirring at a constant rate to prepare apolyester resin composition VIII having an intrinsic viscosity of 0.630.

Comparative Example 9

Chips of a polyethylene terephthalate resin composition IX having anintrinsic viscosity of 0.63 were prepared as in EXAMPLE 8 but withoutdipropynyl methylphosphonate.

Comparative Example 10

Chips of a polyethylene terephthalate resin composition X having anintrinsic viscosity of 0.63 were prepared as in COMPARATIVE EXAMPLE 8except that 0.012 part by weight of antimony trioxide was added insteadof 0.0035 part by weight of tetrabutyl titanate and 0.005 part by weightof dipropynyl methylphosphonate.

The evaluation results of EXAMPLES 20 to 26 and COMPARATIVE EXAMPLES 8to 10 are shown in Tables 3-1 and 3-2.

TABLE 3-1 Catalyst Content Molar (ppm in Properties of the ratio termsof Type of phosphorus % BB polymer Compound α Compound β (α/β) metal)compound 6 hours η EXAMPLE 20 Titanium D 0.009 5 Dimethyl 0.91 0.63acetylacetonate methylphosphonate EXAMPLE 21 Titanium D 0.005 5 Dimethyl0.95 0.64 acetylacetonate methylphosphonate EXAMPLE 22 Titanium H 0.0055 Dipropynyl 0.95 0.63 acetylacetonate methylphosphonate EXAMPLE 23Titanium C 0.005 5 Dimethyl 0.95 0.64 acetylacetonate phenylphosphonateEXAMPLE 24 Tetrabutyl titanate D 0.005 5 Dipropynyl 0.95 0.63methylphosphonate EXAMPLE 25 Titanium citrate D 0.054 8 Ethyl 0.95 0.63chelate diethylphosphonoacetate EXAMPLE 26 Ammonium D 0.054 8 Ethyl 0.940.64 titaniumperoxocitrate diethylphosphonoacetate COMPARATIVETetrabutyl titanate None — 5 Dipropynyl 0.98 0.63 EXAMPLE 8methylphosphonate COMPARATIVE Tetrabutyl titanate None — 5 None 1.210.63 EXAMPLE 9 COMPARATIVE Antimony None — 100 None 1.01 0.63 EXAMPLE 10

TABLE 3-2 Specific Type of No. of resistivity polyester Hue debris ofmelt com- L b (No./0.02 mg) [MΩ · cm] position EXAMPLE 20 60.1 2.5 10510 I EXAMPLE 21 60.2 2.5 3 500 II EXAMPLE 22 60.1 2.6 3 490 III EXAMPLE23 60.2 2.7 3 490 IV EXAMPLE 24 60.3 2.5 3 500 V EXAMPLE 25 57.3 1.5 2080 VI EXAMPLE 26 57.2 1.4 15 80 VII COMPARATIVE 60.3 5.3 3 3 VIIIEXAMPLE 8 COMPARATIVE 60.4 8.6 3 3 IX EXAMPLE 9 COMPARATIVE 56.3 2.5 120120 X EXAMPLE 10

Example 27

The polyester resin composition V was thoroughly dried and fed to anextruder. The composition was then melt-extruded onto a casting drum andrapidly cooled and solidified while applying electrostatic charge sothat the extruded composition is in close contact with the drum. Asingle-layer unstretched film prepared thereby was stretched 3.5 fold inthe longitudinal direction at 90° C. and to 3.5 fold in the transversaldirection at 105° C. to prepare a polyester film having a thickness of10 μm. The film forming ability of the composition was satisfactory. Theresulting film had few coarse projections and satisfactory hue.

Example 28

The polyester resin composition III was thoroughly dried and fed to amain layer extruder of a device for making laminated films. Thepolyester resin composition IV was dried and fed to an auxiliary layerextruder. The compositions were melt-extruded on a casting drum via atwo-layer die and rapidly cooled and solidified while applyingelectrostatic charges so that the extruded compositions closely contactonto the casting drum. A two-layer unstretched film, the mainlayer/auxiliary layer thickness ratio of which was 6/1, was obtained asa result. This unstretched film was stretched to 3.5 fold in thelongitudinal direction at 90° C. and 3.5 fold in the transversaldirection at 105° C. to prepare a laminated polyester film having athickness of 8 μm (the thickness of the auxiliary layer being 1.33 μm).The film forming ability was satisfactory. The film obtained thereby hadfew coarse projections and satisfactory hue.

Example 29

A laminated polyester film having a thickness of 8 μm (the thickness ofthe auxiliary layer being 1.33 μm) was prepared as in EXAMPLE 28 exceptthat the polyester resin composition III was used to form the main layerand the polyester resin composition V was used to form the auxiliarylayer. The film forming ability was satisfactory. The film preparedthereby had few coarse projections and satisfactory hue.

Example 30

A polyester film having a thickness of 10 μm was prepared as in EXAMPLE27 except that the polyester resin composition VI was used. The filmforming ability was particularly high. The resulting film had few coarseprojections and satisfactory hue.

Comparative Example 11

A polyester film having a thickness of 10 μm was prepared as in EXAMPLE27 except that the polyester resin composition IX was used. Itscastability by electro-pinning was not problematic. The film preparedthereby had few coarse projections but poor hue. Moreover, the thermalstability was poor, and the productivity was low.

Comparative Example 12

A laminated polyester film having a thickness of 8 μm (the thickness ofthe auxiliary layer being 1.33 μm) was prepared as in EXAMPLE 28 exceptthat the polyester resin composition X was used to form the main layerand the polyester resin composition IX was used to form the auxiliaryPayer. Its castability by electro-pinning was not problematic. The filmprepared thereby had many coarse projections and poor hue. Moreover, thethermal stability was low, and the productivity was low.

The evaluation of EXAMPLES 27 to 30 and COMPARATIVE EXAMPLES 11 and 12are shown in Tables 4-1 and 4-2.

TABLE 4-1 No. of Polymer debris % Castability composition (No./ BB byAuxiliary 0.02 6 electro- Main layer layer mg) hours pinning EXAMPLE 27Polyester 10 1.01 B composition V EXAMPLE 28 Polyester Polyester 3 1.05B composition composition III IV EXAMPLE 29 Polyester Polyester 3 1.05 Bcomposition composition III V EXAMPLE 30 Polyester 20 1.05 S compositionVI COM- Polyester 3 1.31 B PARATIVE composition EXAMPLE 11 IX COM-Polyester Polyester 60 1.2 B PARATIVE composition composition EXAMPLE 12X IX

TABLE 4-2 Hue No. of coarse projections L b H1 (No./100 cm²) H2 (No./100cm²) EXAMPLE 27 59.1 2.5 37 1 EXAMPLE 28 59.1 2.6 19 1 EXAMPLE 29 59.12.6 23 1 EXAMPLE 30 57 1.5 45 1 COMPARATIVE 59.4 8.6 19 1 EXAMPLE 11COMPARATIVE 57.3 5.5 110 2 EXAMPLE 12

1-19. (canceled)
 20. A polyester resin composition comprising, on aweight basis, 30 ppm or less of antimony, 0.5 to 50 ppm of titanium, and0.1 to 100 ppm of phosphorus, wherein organic polymer particles arecontained in amount of 0.1 to 5 wt %, the organic polymer particleshaving an average particle diameter determined by dynamic lightscattering of 0.05 to 3 μm and containing 0.01% or less of coarseparticles relative to the total number of the particles, the coarseparticles having a diameter at least twice the average particlediameter.
 21. The polyester resin composition according to claim 20,wherein a titanium compound is used as a polymerization catalyst. 22.The polyester resin composition according to claim 20, comprising atitanium oxide.
 23. The polyester resin composition according to claim22, comprising a complex oxide of titanium and silicon.
 24. Thepolyester resin composition according to claim 20, comprising a titaniumcompound having at least one substituent selected from the groupconsisting of functional groups represented by formulae 1 to 6 below:

(wherein R₁ to R₉ each represent hydrogen or a C₁-C₃₀ hydrocarbongroup).
 25. The polyester resin composition according to claim 24,wherein at least one of R₁ to R₉ in formulae 1 to 6 is a C₁-C₃₀hydrocarbon group having an alkoxy group, a hydroxyl group, a carbonylgroup, an acetyl group, a carboxyl group, an ester group, or an aminogroup.
 26. The polyester resin composition according to claim 25,wherein at least one of R₁ to R₆ in formulae 1 to 3 is a C₁-C₃₀hydrocarbon group having a hydroxyl group, a carbonyl group, an acetylgroup, a carboxyl group, or an ester group.
 27. The polyester resincomposition according to claim 25, wherein at least one of R₁ to R₃ informula 1 is a C₁-C₃₀ hydrocarbon group having a carboxyl group or anester group.
 28. The polyester resin composition according to claim 25,wherein R₇ in formula 4 is a C₁-C₃₀ hydrocarbon group.
 29. The polyesterresin composition according to claim 28, wherein R₇ in formula 4represents a C₁-C₃₀ hydrocarbon group having a hydroxyl group, acarbonyl group, an acetyl group, a carboxyl group, or an ester group.30. The polyester resin composition according to claim 20, comprising atleast one phosphorus-based compound selected from the group consistingof a phosphoric acid-based compound, a phosphorous acid-based compound,a phosphonic acid-based compound, a phosphinic acid-based compound, aphosphine oxide-based compound, a phosphonous acid-based compound, aphosphinous acid-based compound, and a phosphine-based compound.
 31. Thepolyester resin composition according to claim 30, comprising phosphoricacid and/or a phosphate compound.
 32. The polyester resin compositionaccording to claim 30, comprising a phosphonic acid compound and/or aphosphonate compound.
 33. The polyester resin composition according toclaim 32, wherein the phosphorus-based compound is ethyldiethylphosphonoacetate.
 34. The polyester resin composition accordingto claim 20, wherein the molar ratio of titanium to phosphorus (Ti/P) isin the range of 0.1 to
 20. 35. The polyester resin composition accordingto claim 20, further comprising 5 to 100 ppm of an alkaline earth metalelement on a weight basis.
 36. The polyester resin composition accordingto claim 35, comprising 15 to 60 ppm of magnesium on a weight basis. 37.The polyester resin composition according to claim 20, wherein theorganic polymer particles have a degree of cross-linking of at least50%.
 38. The polyester resin composition according to claim 20, whereinthe organic polymer particles are a vinylbenzene-divinylbenzenecopolymer.
 39. The polyester resin composition according to claim 20,wherein 0.1 to 5 wt % of a water-soluble polymer relative to the organicpolymer particles is contained.
 40. The polyester resin compositionaccording to claim 39, wherein the water-soluble polymer has apyrrolidone residue.
 41. The polyester resin composition according toclaim 20, wherein the specific volume resistivity is in the range of1×10⁶ to 1×10⁹ Ω·cm when melted.
 42. A polyester film comprising thepolyester resin composition according to claim
 20. 43. A laminatedpolyester film comprising a plurality of layers at least one of whichcomprises the polyester resin composition according to claim
 20. 44. Amagnetic recording medium, comprising the laminated polyester filmaccording to claim
 43. 45-52. (canceled)